As part of this weekend's fun improving the performance of my aging 3-year old machine at home, I found that I could upgrade to modern day CPU performance for not that much $.
My main machine at home is a 1.4 GHz Dell Dimension 8100. Apparently these machines were built with pretty good componentry, including PC800 memory. Unfortunately, the CPU was Intel's 423 "Willamette" version, which was quickly replaced my a new incompatible form factor (the 478 pin "Northwood".) If I were to stick with the 423 form factor, I'd only be able to go to 2GHz, the fastest Intel made in that form factor.
However, Google quickly lead me to PowerLeap, which offers an upgrade kit consisting of a socket converter and 2.8GHz 478 pin CPU for only $249. A 2.6 GHz upgrade is only $219. Doubling my CPU speed for $250 sounds like a heck of deal. I have it on order, and I'll post here what my experience with it is.