I have a Compaq 5900Z, circa 1999, runs on W98. My question is, can I simply buy another motherboard and AMD processer and replace the one that is inside the system now, reconnecting all of the components (video, sound, drives, etc. myself). Thanks for your help.

A lot of these oems use proprietary cases and puny psu's so you have to make sure that they can support the new board and cpu that you are planning to get. Current cpus require more power to run than the older generation of cpus. Also, if you are reusing the video and sound card, make sure the board you are getting is compatible with them. I mean, if your card is agp, do not get a pcie board. And finally, when you change motherboards, you will have to reformat the hard drive and reinstall windows using a regular retail copy of windows(your system recovery disk will not work on the new board).

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I had thought about some of those things, but you raise some very good points, especially about having to buy a retail version of Windows and the power supply issue. Doing the math, this won't work for a couple of hundred bucks (I wasn't looking to make it into a super-gamer PC or anything). I really appreciate your help.