Another consideration is the following. Service Pack 2 does install on Windows XP OEM versions, i.e. those that came with a computer and are tied to that computer. But if you run into a problem, these OEM versions usually cannot do repair installations. Often they only allow you to erase everything entirely and start from scratch. In other words, with only an OEM install CD, you run the small additional risk, should the SP2 installation go wrong, of either losing your installation and having to start all over or having to buy a full version of Windows XP.