Possibly first to be released,
Atleast around christmas-ish, I had my first working stuff up and running, and another person who's asked questions on these forums has also got some work done on another game shortly after.

I stopped my work as soon as it surprisingly enough got announced for US release (Though, I suspect that I sometime after US release might go back and do a little mix'n match for the JP version, depending a little on any evt. US cuts/edits).

If anyone need some basic pointers, here's some very very basic info that'll probably make anyone skilled shake his head in boredom, but probably atleast get anyone who's interested started;

1: Many PSP games uses system font, this is the lovely internal hardware font of your PSP. So far, every game I've looked at with Japanese text using this font has been stored in a table similar to EUC-JP and is fully acceptable to completely regular text written over it. As a bonus with the system font, you also have a free VWF.

2: If the game stores text in it's exe, then it's the BOOT.BIN (and not EBOOT.BIN) in the PSP_GAME/SYSDIR you want to edit. To then either overwrite the EBOOT.BIN with it or use a loader or custom-firmware's "Load BOOT.BIN" option to run it.

3: Use UMDGEN to rebuild the ISO of the UMD.

As a side note ports from other platforms (i.e., games that aren't built up from ground on the PSP, but usually originated from PSX or PS2) seems to mostly use their original file structure and formats, with the most noticeable difference being that movies are now stored in h264 video and most audio streams are changed to some odd Attrac3+ variation.

[edit]
Almost forgot, some games seems to store their system messages (SAVE/LOAD yes/no confirm/cancel and EXIT GAME) in the game itself, while others seems pull those from system firmware (not depending on language setting). At the moment, I still don't know how to change which language it calls from the firmware (or locate the messages). Worst case scenario, one could evt. have a custom firmware that has the JP system messages overwritten with the language of choice :/

ToP FVE is almost exactly the same as the PSX version except it doesn't store the data in a VFS. With no PSP ASM hacking capability, forget it... ToP needs ASM hacks to look good. Plus I don't have a PSP or very much desire to own one.

And I'm still waiting for one of our ASM hackers for the PSX version to find the time to get that annoying ass 16 characters/line limit hacked out of the dialogue routine. Sigh... we've had a VWF implemented for 3 years now. :(

So far, you can use a PSP with this tool to debug games on your PSP. And yes, for TOP the files are almost the same.
But they optimized the code a bit :
PSX : 
PSP :
(just an example)

@soluzar : do you have more info about it?
edit : found

Hmm... I tried copying the data files from MegaMan Legends into Rockman Dash PSP, but it hung at the loading screen \
Still, I used files from the PC version, so maybe tomorrow i'll try err... accquiring a PSX version and copying off that.

one thing about ToP is that the main feature is the FULLY VOICED PART. At this point it becomes easier to learn Japanese then try to record all the dialog professionally.