Upgraded hardware to Athlon II X2 245 CPU on a Gigabyte MA-785GM-US2H. This CPU overclocks nicely (and the DDR2 overclocked also.)
Then upgraded to a Phenom X6 1090T with 8Gb of DDR2 1066. Ended up buying a new Antec Solo case to get the heat and noise under control - very nice case. (I feel no need to overclock this chip.)
Tried to upgrade to Ubuntu 10.04.2 LTS amd64 and FAILED! (Funny, the live disk ran fine!)
Then upgraded to Debian Squeeze 220.127.116.11 amd64. (I took a hard look at Archlinux and may still give that a try later.) All working very well - I seem to conveniently forget how much custom software I have to install and compile every time I do this.