Ok, i have a psp when it first came out and i now have custom firmware 3.40 on it. Now my brother is getting one and the chances are it will be the new slim and lite. is there any custom firmware for it so it can run iso games. also if it happens to be an older model can you install custom firmware from any of the official firmware?
Thanks

Yes you can run custom firmware on the slim you will need to make a cemetery battery v3 and that will require a fat psp with custom firmware to install the cemetery battery. Latest custom firmware on the slim is 3.71m33-2, still a bit unstable imo.

what do you mean unstable? what is wrong with it?

Also does it matter what firmware the slim and lite is on?

And does it matter what motherboard the slim and lite has like it did in the original psp?

3.71m33-2 will give you an unrecoverable brick if you modify the flash. NO it does not matter what psp firmware the slim as long as its above 3.60 because the slim wont work on firmware lower then 3.60. No the motherboard is not an issue when installing custom firmware.

what do you mean by unstable then?

Bugs such as if you were to mess around with the flash files you brick the slim and you cannot use pandora or the cemetery battery to restore it. Also there are some iso that doesn't want to work and will crash randomly during gameplay.

There is a fix for the USB flash bug: http://www.psp-spot.com/forums/index.php?showtopic=48534
I don't know about unstable ISOs; I'll have to try a few when I get more time.

M33-2 fixes many of the issues with M33. Yuor only options on the slim are 3.60M33 or 3.71M33 anyway.