Here's a size comparison of the DS and PSP whicih was shown on IGN.
On it's own, the PSP usually looks big, but compare it to the DS, its roughly the same size (infact, PSP looks smaller). The PSP has a
much better screen, its bigger and clearer, instead of two small ones.
The DS isn't much bigger than the GBA
So comparing these, the PSP shouldn't be too different size wise from the GBA
