I have 3 computers running a debian "distros" and another running Windows 2000. I am losing time when i execute a programs (waiting a lot of time and i not have a time). i use a lot of programs, nearby to ten or eleven, and my CPU is hot. ;)
Your best bet for clustering under Linux is Mosix (http://www.mosix.org). Mosix dynamically moves each process to the machine with the largest available resources. That's the best you can do without writing parallelized code.
Clustering across OS boundaries is not possible (unless of course you run VWWare on Windows and install Debian Linux).