I just went through the process. Since the display and I/O gear was OK, I only needed a tower. Bought the parts from Fry's and online.
AMD 2600+ Barton uproc 333Mhz FSB, 512K Cache, with heatsink and fan, 512MB DDR RAM, Shuttle Ultra MB, 80GB Maxtor HDD, CD/DVD, CD Writer, 128MB Nvidia chipset graphics card, Alaska tower, modem, added an extra cooling fan, etc. With rebates comes to $474. Runs like a champ. One heck of an improvement over my 233Mhz system from which the only thing I salvaged was the floppy drive and a "Dilbert" sticker for the front.