No-one should attempt this in a household oven, for various reasons:
1. Both lead and tin are volatile when heated. Specifically, this means that lead oxide and other dangerous chemicals are emitted when lead is heated.
See:
http://www.sentryair.com/solder fume.htm
2. The fluxes used in production of modern electronics are designed to remove oxides very, very efficiently. They are NOT designed to be biocompatible. Small amounts of residue may still be on the board.
3. Boards may contain parts which will melt at the reflow temperature. These components are generally through-hole and added as a separate step.
So, basically, once you have completed this operation and (possibly) fixed your video card, BUY A NEW OVEN.
The other option is to buy a cheap toaster oven and use it only for reflowing however, thats cost prohibitive.