Dell has a 2.4 GHz celeron computer with 256 ram fopr 300 bucks and I was wondering how this would work with a PVR-500 and Knoppmyth?

It'd probably be OK. If it's the same one that they had listed over at Hot Deals Club, you'll definitely want a bigger HD (+~$100), and it's only got a CD-ROM drive (+~$45 for a DVD burner), and the memory is a bit lean. Also beware of potential problems with a USB keyboard (I didn't check which they provided). Finally I suspect that you'll want to add am Nvidia video card if you want to do TV-Out (+~$45)...