Combined-Knowledge provided me with a lovely laptop when I recently taught the Mindsharp Upgrade course. It was a Toshiba Portege M400 Core 2 Duo T7200 (2.0 GHz) with 4 GB of RAM. I used it to run the virtual machines to demo the medium server farm in-place and gradual upgrade processes. One thing I noticed was that the machine was not optimized for dual processors, see "Windows XP Multi Core config - Does your OEM do it for you?". Other configurations to note with multi-core machines are:
Note: Although I do have a SharePoint medium server farm virtual machine configuration, I do not use this setup for day to day experimenting, as better performance is achievable when the web server and database are on the same virtual machine, see: Virtual Server Technical Library: Improving performance.