Two things I'd like to add.

Quote Originally Posted by Blodrast
Yes. Vmware or some similar virtual machine software will do the trick.
I'll prefix this with my knowledge of VMware is at least a year old, so I could be wrong at this point, so please keep me honest mate. This is an excellent suggestion for DOS games, this or DOSbox work wonders. However, unless they've changed it, VMware is not very well suited for modern 3d gaming. The reason is VMware simulates "virtual" hardware to the guest operating system, thus fooling it into thinking that there are other devices installed. The video adapter that the guest OS sees was some special hacked-up adapter that can do some very rudimentary DirectX API operations at best. So in other words, one couldn't simply install a guest OS, and the install their ATI/Nvidia drivers inside the guest OS. I do remember reading that VMware was working on some advanced DX support, but it's been a long time. Again please correct me if I am wrong here.

Quote Originally Posted by Tosainu
Wouldn't it be possible to just create a dual boot? One running the drivers for card 1, OS install 2 running the drivers for card 2. I don't think a virtual machine is required, that will only slow it down.
This is a possibility yes, however I personally would not recommend it. Dual booting two versions of Windows is often a tenuous operation at best, and based on my experience at home and work it's not something I'd recommend to anyone anymore, unless there was some dire temporary need. Driver installations can conflict (even when on separate partitions), application installs get wonky, user settings sometimes automagically "migrate", and a host of other wierd activities that we could never find adequate documentation or explanations for. I am aware of others who have dual booted Windows variants with varying degrees of success, but again, in my personal view, I would not recommend this to anyone except as a temporary measure.

My $0.02 USD friends.