If you head to ATI's website, you can download the latest Catalyst driver they offer. I'd start there. I have a 2400XT in my server machine, and it runs games like BF2, and the like with settings set reasonably high. I also have a friend who uses his 2400XT to play World of Warcraft with setting set somewhere around 80% at 1024X768 resolution. I've never bothered to try and torture myself by running AH2 with the card, though.
Here's the link to amd/ati's web site. Just indicate your OS and select your card from the list on the right:
http://ati.amd.com/support/driver.htmlThere may also be 'specialty' drivers offered by tweakers somewhere on the web, but I doubt you're going to get too much of a boost based on the underlying technology that you're dealing with - the 2400 just isn't a 'serious' gaming card. Keep your expectations modest, and you should be fine. Hope for too much and you're probably going to be disappointed.
