Well its a bit like a Nvidia 7600, with all the ram stripped out and the core crippled. The 7600 is a bit slower than an ATi x1800, so going by that, I imagine the 7100 will be a bit slower than the x1600, which is the Recommended GPU, but it'll be faster than a 9600. I think.
If you go that route AFAIK the 7100 will share your system memory, so get a load of that in when you're speccing your PC up so you don't cripple it any more than it already is.
Why you'd want to do any of this when you can pick up something cheap like a HD4650 for as little as 40 quid is beyond me, as the 4650 will certainly blow a 7100 out of the water.
