I think you're better off putting together the hardware yourself. In order to make good use of DOS, you really need to know things like what IRQ's are free, and how to arrange your conventional memory and such. If you're going to go the hardcore route, then you might as well go all the way and learn how to do it properly.

Installing hardware really isn't all that hard. It's usually just a matter of stuffing the card into the computer and loading the appropriate driver. Most drivers are still readily available on the internet, even though they're 20+ years old. The main hard part is sound cards, where you need to know IRQ, DMA, I/O addresses, etc. With some cards, this kind of stuff can be set with jumpers (you might need to find a scan of the manual on the internet to find out what jumpers are what)... otherwise, sometimes the easiest way is to just guess at values until a game works, then write down those numbers on a sticky note that you keep on the computer itself so you don't forget 'em.

--Zero