The 9600GSO, with 96 shaders, is an OK video card for folding, though it's easy to bog it down. On 511 point WU's, mine drops down to ~3000 PPD, and mine has a stock shader speed of 1700 MHz which I've overclocked to 1850 MHz, compared to the stock 1375 MHz on the card you're looking at
On 787 point WU's, mine does about 4200-4500 PPD,
on 353 point WU's, it can do about 4600 PPD, but it also varies a lot and can be as low as 4300.
I forget how it does on 1888 pointers, but I think it can take the thing 14-15 hours to complete one, so not great.
Of course, all of those numbers are on a Windows 7 install which is running... quirkily, and I'm also running notfred's on there, so it's not necessarily ideal.
It also looks like the $20 rebate your card advertises is applicable only for one card per household, so if you buy more than one you'll only get one rebate in total, unless you get friends/family to buy the others for you.