Buy a Dell refurbished desktop for about $400, you can't build one as cheap as you can buy one of those refurbished pc's. I just built one from scratch and paid $500 and that did not include the Windows operating system.
Dell has one for $424 right now. You get 2.4gig cpu, 500mb ram, keyboard, mouse, Windows XP, thats a pretty good deal. Thats pretty much what I'm running. For a monitor shop your local used computer store, old monitors exist in huge numbers. I got a nice 17 inch sony trinitron for only $75.
I agree with others on the parallel port card. One thing for sure, people should test all the pins on the parallel port. My built in port (brand new Intel) was whacko, pin 13 (an input pin) had 5vdc and my Z stepper refused to work at all. Two other people I heard about had problems recently with theirs also. I installed a cheap made in china parallel port card (CompUSA) and it works perfectly.
http://outlet.us.dell.com/Dispatcher...rcDetail=offer