6 months to 1 year is my limit for an aging PC although I let the kids go longer or they start bitching about poor performance.
Currently have running:
Athlon 64 3000+ PC
Sempron 64 2800+ Laptop
Athlon 2600+
Sempron 64 2600+ **FOR SALE** LOADED PC (UNUSED)**
Its so easy to just swap Mainboards and CPU's that I look forward to new technology.
Windows Vista will be delayed until next year so there are no O'S upgrades to do until then.
Gary