You will need a new card to run AH2. Here's a link to pricewatch where you can look at prices on various cards.
http://www.pricewatch.com/menus/m37.htmThe absolute minimum card to get would be a GeForce2 MX400 with 32 MB. That is the card I currently have installed on my work machine and it will run AH2, but texture sizes have to be turned down. It would be the cheapest card to get, but it's not the best value.
Here are some prices (shipping included) for cheap cards to consider.
$26 - GeForce2 MX 400 w/32 MB - absolute minimum
$28 - Geforce2 MX 400 w/64 MB - 2 bucks more for double the memory is well worth even if you're going for the cheapest card possible.
$37 - GeForce4 MX 440 w/64 MB - Better performance for only $9 more.
$46 - Geforce4 MX 440 w/128MB
$54 - GeforceFX 5200 w/128 MB
You can find some benchmark tests for the above cards in these articles:
http://www20.tomshardware.com/graphic/20030120/index.htmlhttp://www20.tomshardware.com/graphic/20031229/index.html