You should check what kind of graphics slot your motherboard has. Given its age it's most likely AGP, which would mean your options are pretty limited. Here's
Newegg's list of AGP graphics cards. Assuming you plan to use Decal, you should get a card with at least 256MB of RAM.
According to a
Tom's Hardware article from a year ago, the
Radeon HD 3850 512MB is a good AGP card for ~$100.
The
Radeon HD 4650 1GB is another option at $70. Contrary to the higher product number, it's not as fast as the 3850, but the difference may not be noticeable playing AC on an old computer.
The
Radeon HD 3650 512MB looks decent for ~$60, and is probably good enough for AC.
If you go much lower than $60, then you start to get into cards that aren't made for games, and aren't much better than integrated graphics.
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[LotRO] Digero (Guardian), Digrim (Burglar), Dignite (LM), Azrea (Hunter) - Landroval
[AC] Digero, Lyera, Draxxe - Leafcull (Retired)
[CoH] Devil's Zealot, Scinta, Izzard - Guardian (Retired)
Digero's AC Decal Plugins:
http://decal.acasylum.com
