http://www.videoguys.com/DIY-GPU.html
Yeah to add to their list the new Avid Xpress HD and the other one (forget it off the top of my head) also have vpu-assisted rendering for the output, IIRC they are nVidia centric. I know Liquid like ATi and the new Xpress like Quadros, but I'm not sure if that changed and Avid's added better ATi support or not for the new Express products.
(IMO, check their forums, they would know the current state of affairs/support).
Overall though I've heard the effect is still minimal.
The thing everyone seems to be waiting for is for some kinda of CTM or CUDA plug-in to allows the SPs to be used four encording, rendering, and transcoding, etc. Then it should be a simple code.
IMO, he shouldn't get a Gf7 series if he's serious about photoshop, he should stick to the newer GF8s or the X1Ks or wait for the new HD2xxx series with their colour support, especially if currently on a CRT or for a long term build that might involve an LEDlit LCD.
I have a feeling that the wisest long term solutions are the HD2600 or the GF8600, although if $500 is the limit and heat isn't an issue and power consumption isn't a huge concern, then the power of something like an HD2900XL might be nice, howeve is alot more card than is needed under current implementations.
And while it's not a current issue, I'd want to ensure support for all playback features as well, so even if going with the GF7 I'd make the GF7600GT the bareminimum, but like I said I'd prefer the newer solution, especially for photoshop in particular.
If 3D animation were involved then I'd be more inclined to include the GF7s, but for what's listed above the X1K, GF8, and HD2 cover pretty much all the bases, and even through the price ranges, but I'd wait for the Gf8600 prices to come down a slight bit first, and also to see what the HD2s have to offer. But if he can't wait, I'd say get the passive GF8600s since gaming isn't an issue at all.