OK, as promised here are the instructions to load the game.
I personally find this a bit over the top but it was requested. Right now the game is not playable due to a StackOverflow, furthermore the movies are black due to some unknown reason!
Before you start you have to make sure you decrypted the eboot.bin (on your PSP) and replaced it in your ISO. As this is a common thing to do on all the new games it is not covered here.
You also need a REAL PSP with CFW running to decrypt the data files for Kingdom Hearts: BBS! There is no way to decode them on your PC! Of course this is also true for decrypting the eboot.bin but I mention it again!!!
INSTRUCTIONS:
1) Edit the starting batch file for JCPSP and insert the "-Xss12m" switch on both the command line (I marked the second one)
2) Load the UMD in your UMD Browser and Run the game
3) The emulator shows you this message
4) Close the emulator, make sure you have at least 500 MB free space on your PSP's memory stick and then copy the JpcspConnector directory from the MS0\GAME directory to your PSP into the PSP\GAME directory, also the 2 files as mentioned in the message to the \TMP directory.
5) Run the JPcspConnector on your PSP
6) It shows you the Decrypting ms0:... message, wait for the app to end and copy/move the decryted file back into the directory on your PC (as stated in the message before)
7) After that start the load the UMD again in JPCSP and it shows you the second file
8) Copy the new files to the PSP, run JPcspConnector again and then move the .decrypted file back to the PC, again run JPCSP for the third file
9) Repeat the decryting and then start JPCSP again
10) The settings are mostly the default settings, I also activated the media engine (you don't have to)
11) You're ready to start the game
NOTE: This whole procedure will only work with a clean ISO from your UMD, not from the many hacked/patched/whatever copies that float around the net! The decrypting of the encrypted data files work 100%
r1773
Use the -Xss10m (or -Xss11m, -Xss12m, ...) switch or you're ending up in a stack overflow right at the start
You can also activate the Media Engine but right now it's pretty useless because the movies are still black.
You can say all things said in the JAP version are also true for the US version: The movies are black, you have to be real quick to see a bit more of the game but you run into a stack overflow error sooner or later! There are also various graphical errors.
r1791
The -Xss switch is no longer necessary, the stack overflow errors are fixed.
Use no compatibility settings except Media engine on.
Just in short: The game now seems to be playable or at least half-playable. The movies are still black, have to be skipped. There are various graphical glitches. I noticed now the text in the tuturial is not visible (or black), it surely was so before but I did not notice it because of the StackOverflows.
r1793
Only a small update: The movies are now played but they are still very jumpy
r1796
Another small update: The movies now play very well with the Media Engine enabled
r1800
Major problem found by Pingutino: Saving does not work on all revisions. Right now there is not much you can do. I forgot to test this because you have to play a while to get to a save point. Sorry
- Good thing it's still in the half-playable section 
I personally find this a bit over the top but it was requested. Right now the game is not playable due to a StackOverflow, furthermore the movies are black due to some unknown reason!
Before you start you have to make sure you decrypted the eboot.bin (on your PSP) and replaced it in your ISO. As this is a common thing to do on all the new games it is not covered here.
You also need a REAL PSP with CFW running to decrypt the data files for Kingdom Hearts: BBS! There is no way to decode them on your PC! Of course this is also true for decrypting the eboot.bin but I mention it again!!!
INSTRUCTIONS:
1) Edit the starting batch file for JCPSP and insert the "-Xss12m" switch on both the command line (I marked the second one)
2) Load the UMD in your UMD Browser and Run the game
3) The emulator shows you this message
4) Close the emulator, make sure you have at least 500 MB free space on your PSP's memory stick and then copy the JpcspConnector directory from the MS0\GAME directory to your PSP into the PSP\GAME directory, also the 2 files as mentioned in the message to the \TMP directory.
5) Run the JPcspConnector on your PSP
6) It shows you the Decrypting ms0:... message, wait for the app to end and copy/move the decryted file back into the directory on your PC (as stated in the message before)
7) After that start the load the UMD again in JPCSP and it shows you the second file
8) Copy the new files to the PSP, run JPcspConnector again and then move the .decrypted file back to the PC, again run JPCSP for the third file
9) Repeat the decryting and then start JPCSP again
10) The settings are mostly the default settings, I also activated the media engine (you don't have to)
11) You're ready to start the game
NOTE: This whole procedure will only work with a clean ISO from your UMD, not from the many hacked/patched/whatever copies that float around the net! The decrypting of the encrypted data files work 100%
r1773
Use the -Xss10m (or -Xss11m, -Xss12m, ...) switch or you're ending up in a stack overflow right at the start
You can also activate the Media Engine but right now it's pretty useless because the movies are still black.
You can say all things said in the JAP version are also true for the US version: The movies are black, you have to be real quick to see a bit more of the game but you run into a stack overflow error sooner or later! There are also various graphical errors.
r1791
The -Xss switch is no longer necessary, the stack overflow errors are fixed.
Use no compatibility settings except Media engine on.
Just in short: The game now seems to be playable or at least half-playable. The movies are still black, have to be skipped. There are various graphical glitches. I noticed now the text in the tuturial is not visible (or black), it surely was so before but I did not notice it because of the StackOverflows.
r1793
Only a small update: The movies are now played but they are still very jumpy
r1796
Another small update: The movies now play very well with the Media Engine enabled
r1800
Major problem found by Pingutino: Saving does not work on all revisions. Right now there is not much you can do. I forgot to test this because you have to play a while to get to a save point. Sorry
- Good thing it's still in the half-playable section
JPCSP games tested with Athlon X2 4850e, 4 GB RAM, Radeon HD 3300 (onboard), OpenGL: 3.3.11653, Windows XP SP3 32-bit
PPSSPP games tested with Intel i3, 4 GB RAM, Intel HD Graphics 2000 (onboard), OpenGL: 3.1.0 Build 6.14.10.5421, Windows XP SP3 32-bit
PPSSPP games tested with Intel i3, 4 GB RAM, Intel HD Graphics 2000 (onboard), OpenGL: 3.1.0 Build 6.14.10.5421, Windows XP SP3 32-bit