Assuming you've tried this with little or no success already, you'd need a new CPU.
Which means a new mobo. Which means new RAM.
The cheapest options which will get the job done are...
- only real rule with RAM: if you intend to run it at speeds higher than, oh, 800MHz, you should probably buy sticks with a cooling solution.
PSU-wise, it really depends on how decent the one you have is. That CPU/MOBO/RAM combo shouldn't really push any decent PSU too far.
If you want to play it safe, here's a cheap PSU
which will more than do the job.
As far as video card goes, that has almost nothing to do with Photoshop performance, so it's moot.
edit: If you're just looking for a video card which will fit your budget and system, that'd be the 5750/5770, depending on what prices you can find.