after writing i checked this is too far out because of pricing i guess but....i wrote and now i post it 🙂 ....Shuttle has great barebones like the Shuttle XPC SN95G5V2 AGP nforce3 ($280) and Shuttle XPC SN25P ($350.00) with Nforce4 and Pci-e. These Socket 939 barebones have the whole feature set of a pre-built SFF, but it comes without a CPU (lets say a Winchester or Venice 3200+ for 170-200$), HDD (like a Samsung SpinPoint P120 200GB SATA II for 90$), optical drive (for instance a dual-layer dvd-burner NEC ND3540 or LG 4163B for 60$), Memory Modules (eg 2x1024MB sticks, Ram is very cheap at the moment, a single Stick of DDR 400 PC3200 memory with CL 3 or 2.5 costs only 80$, Socket 939 can use dual-channel, so two cheap 1024mb sticks would be nice) and a graphics card of course. Honestly i dont know what kind of graphics card is necessary for photoshop stuff, but if he doesnt want to play games at all then a ATI 6600 non-GT ($115) is fine. They are available for AGP and PCI-Express. Overall about ...erm...$700-1000, depending on the options. But i guess u wanted a cheaper system? And pre-built?...i know, but to me it seems, that u can make a better deal when u DIY..
PS: another suggestion is to buy a sff with nforce2 chipset and a Sempron 2400+, should help decreasing overall prices... models: Shuttle XPC SN45GV3 ($200) or a Soltek QBIC EQ3705A ($200).