The machine you listed in your first post will be fine for what you want to do, I can easily navigate photoshop with 3 gig of ram on an Amd 64bit 3200 running at 2.2 gig.

I run a 250 gig sata drive for windows and instlled stuff, I run a 160 IDE drive for programs and documents.

This is easiest for when windows spits it's dummy out and needs to be reinstalled, however I have a 500 gig usb drive on top of the case for backup's.

Witha good cpu setup you shouldn't feel the need to overclock the cpu unless you really want to push the boundaries of what you can do with a cpu, not forgetting the cooling aspect of it of course.