I eventually broke down and bought a nice new PC. In fact I bought two of them, one for me and one for my better half. They are identical AMD64 boxen, with 1Gib of RAM and 160Gb of disk space, nvidia graphics card and 17" iiyama TFT monitor.
My machine is running Debian "Etch" pure-AMD64, so 32-bit code runs in a chroot. Once OpenOffice.org2 makes it into Etch I'll swicth, and get rid of the chroot. So far the only problems I've had were installing the nvidia kernel, it works, but was awkward to do, and xine won't play MP3s - it segfaults.
The real challenge now is to install/configure the second machine for my better half. Debian AMD64 isn't complete enough for her, the chroot for OO.o and other missing bits will annoy. I think I'll probably install Debian Sarge, with a 64-bit kernel, and 32-bit userland. This combination should be fast enough, stable enough and feature complete. I'll then be able to decommission the last Windows machine in the house.
Now I have a proper desktop system, I can get back to Perl...