im using nVidia nForce 2 with intergrated nvidia geforce 4 MX 440 64mb. can i disable the card and install an ATI Radeon 9800 XT card or do i have to stick with nvidia cards only?
You're fine, as long as you have an AGP slot which you will I don't think any Nforce 2 boards don't have AGP, it doesn't matter who makes the card, you'll be able to disable the onboard video and just pop in the 9800xt.
Well for one thing don't get a 9800xt, they're a HUGE waste of money. For $200, get a 9800 pro, it's only a tiny bit slower, or for closer to $220, get the 6600GT AGP, which is and Nvidia but way faster than the 9800xt and keeps up with even the $400 level cards easily.
Oh well you'll be fine with a 9600 as they don't take up much power. As for XT and pro, each series of Radeon goes by the following types:
XT>Pro>(this will just have the name of the card, no additional letters i.e. 9600, sometimes called np or non-pro)>SE or Sucky Edition, SE's are usually severly crippled and much slower versions of the cards and should be avoided
So the 9600xt is the best 9600 you can get, get the 256mb 9600xt and it'll run great, although just to mention the 9600xt isn't much faster than the 9600 pro but doesn't cost too much more anyway. Pretty much the 9600xt's core is clock 100mhz faster, but I'd get the 9600xt 256mb.