Chris,
The Server only serves! The video on the server only need to be enough to install WHS, no more. In fact, the design of some WHS servers have no facility for video at all, no KVM connections, nothing. All your media processing is either done by the CPU - if you're transcoding on the fly, or by the Client computer.
Although many people have done the same as you, that is utilise old stuff to repurpose to a server, don't forget that this IS a server and is based on Server 2003, so any drivers you might need for your setup should really be 2003 versions.
Good luck with your setup.
Colin