When going to all the trouble of replacing the CPU, a few other upgrades can be done at the same time:
- Upgrade RAM to 2GB maximum (required for OS X Lion), for example, Crucial CT541128
- Upgrade internal 2.5" SATA hard drive to larger size, and/or faster 7400 RPM or SDD.
- Replace PRAM battery with a fresh one (CR2032 lithium 3V)
The battery in question for this model of Mac mini (and many other Macs and PCs) is a CR2032 lithium 3V.