If you still have the valid key, you may be able to call/email Microsoft and be able to purchase or at least cover the cost of postage for new CDs.

I think Vista was the first M$ O/s to have all the versions on the same DVD (while used for upgrading purposes, could be used to install on other computers if they'd lost their own Copies - but still using the their own Serial)... get what I mean?

Little surprised that some computers actually had XP MCE, wasnt your typical mainstream purchase option.