As far as PSU:
I had an Intel Celeron D 360 (3.46GHz), 2GB DDR2-4300RAM, an ATi Radeon X1650 Pro (somewhat OverClocked), a 7200RPM Seagate hard drive
(the maker escapes me )
, a Memorex DVD\CD-RW and a Sound Blaster Audigy SE powered by a 430W Mad Dog Multimedia PSU, and it wasn't cutting it. But I do extra hardcore insane gaming, so I kinda push the limits of everything. It was fine on my Intel Pentium 4 Willamette 1.6GHz, 768MB-DDR RAM, dual Western Digital hard drive, ATi Radeon X1300 setup, but newer computers and hardware (obviously) need more juice.
As far as a GPU (graphics card):
I have had a horrible (personal) experience with nVidia (I have another name for them, but Ill save that for another time
) and I have converted over to ATi 100%- no problems at all (all 4 computers in my house are ATi, no problems at all with them). Including overclocking them (using ATi Overdrive, not the old fashoned way).
As far as CPU:
As I recall, Intel is faster, but AMD has a larger on-board cache. Just depends on pricing and what your needs are, I guess.
Photo editing takes lots, and if your going for Vista, a lot more. I use (on boot time with vista) about 28% of 2GB
Get at least 1GB, preferably more if your going to get really large files and lots of programs open.
I can't help much more myself, I haven't moved comfortably into the motherboard market yet, but just make sure that you have what you need, and then some. It always helps to have more then you need, as opposed to needing more then you have!