PS2 - PSP comparison
It's the same game.
-Same level design
-Different level of graphics (though it doesn't strike me as too far off)
-Lock-on is mapped differently (R2 in PS2 version, R+D-pad down in PSP version) and block relies entirely on holding down square (the PS2 version allows you to block by either holding L2 or square)
-Force Unleashed mode. This is where the PSP tosses in Historic Missions, Force Duels (1v1 versus a force user, including ones from EU), Order 66 (survival against waves of enemies) and Force Out (No idea what it is as I haven't unlocked it yet)
There you have it. The PSP version has the Jedi Temple stages as well.
I say the PSP version is more worth the time and money, because it has more content than the PS2 version and it is portable, but it may be easier to play on the PS2 version for most people.
Figured you'd want to know the differences ^^