I'm in the process of repurposing my gaming rig to a dual-boot system (XP-64 and Server 2008). Looking at the HCL, I didn't see my 8800GTS-640 listed, but the Windows Default Drivers did work for my test install of Server 2008. I'd think that pretty much any standard graphics card would work for you.
I believe any recent card with Vista x64 drivers should work or the default Windows drivers. I haven't worked with Server 2008 so I really can't offer much more than that.
I bought a raft of 8500GT's for my servers just to improve graphics performance over the integrated cards. The drivers from the CD that came with the cards worked perfectly on Windows Server both 32 and 64 bit versions (both included on CD). They are very cheap cards and perform well under office conditions.
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