In order to take the computer back to factory condition, you'll need to use the Recovery options offered by the Recovery Partition or the Recovery Discs that you created or purchased. Have you done that? If not, then you'll need to perform such a Recovery which would include the Media Center portion.
Simply reinstalling XP Pro from a standard XP Pro disc will do exactly that.. Install only XP Pro.
Hope this helps.
Grif
ok heres the deal i had a hp pavilion dv2000 pc with in xp pro media center ed loaded in it, i reinstalled xp pro however it is no media center ed, i have all the drivers i need but 2 the wireless and the network controllers, i have checked the hp site but none of the drivers listed on the site seem to help, my wireless drive is a broadcom 802.11g wireless network adapter and my other ethernet adapter is a nVidia nforce 430 (MCP51) lan controller i cant find these anywhere could someone please help

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic