You do not need a supercomputer to run a island. Its often enough to use some older computers beacause the server software do not need to run any graphics. We use a MySql database on a OPENSuse installation.
We have tried out a windows XP installation and it works well.
Right now we use the XP machine to run another flavor of Opensim the Realextend software Real extend homepage
Usable: Running the development islands, the OSGrid island and also its a small render farm for Pov-ray images and it runs a webserver that we can do experimental stuff on.