Agree with the previous poster re: OEM versions.
Remember Win XP needs activation (on-line or by phone) after a reinstall.
So even upgrading some components in the future can cause problems with activation, ESPECIALLY if you've an OEM version.
It works exactly as a retail, same updates etc..., but beware if you regularly swap/upgrade components.
I'd personally recommend a "corporate" version - no activation ever, & can be installed on any amount of PCs.
Only proviso is you must own a "corporation"
