No unconnected Ethernet cards (disable if not connected to a cable/hub)
Turn off all non-essential background processes in Windows
Thing that wont work:
Any Windows 64 bit install
Any non-parallel port pulse card or control (e.g. Smooth Stepper, USB drivers, etc)
Laptops (even with a parallel port)
We watched for deals on components on sites like slickdeals and built our PC from scratch. We went a little overboard. This pc is more than you would need.
We went with a solid state drive as our primary drive. We have 4 GB of ram which is more than is needed, but it was a package deal. The PC is fully booted in less than 15 seconds, it runs very cool and it is stable and reliable.
Older HP and dell systems that you can find on Ebay will work just fine. Although this system is on the high end of what you need it was still affordable with building it ourselves we only spent $250.00 on the system with the monitor, which is pretty good for a brand new system of this caliber.