I'm using a PicoPSU 120W for over 1.5year (along with Ian's ATX adapter), that powers my full A1200D PPC along with all the things you see on my signature. No problem @ all and everything works like a charm.
As Delshay said... the only thing you should worry about is the heat. Adding 2xmini VGA heatsinks in the 2 hot components (the yellow square) plus a mini fan blowing air to the PSU and you're set! You can check some pics of it inside my A1200 if you click on the link in my signature.