A quick way is to boot from a floppy, browse to the i386 directory on that cd from your friend, and execute 'winnt.exe'. This will start the xp installer. However, this will just re-install Media Center again. Why does your friend want that machine re-installed? It might be better to fix the problem that just wiping the system.
You can get bootdisks from www.bootdisks.com. The win98 version works fine. Also, add smartdrv.exe to the bootdisk. Run this file before running winnt.exe. It will dramatically speed up the install time. Here's a link to smartdrv.exe:
http://www.vetusware.com/output/wfaxukie/SMARTDRV.EXE