dont format.
install Kaspersky AV or Active Virus Shield -> Scan.
then use Tune-Up Utilities 2007 & clean the registry, Disk drives...
if all these dont help, then run the
Standard Recovery, this way only Media Centre is re-installed, this process does NOT affect any data on other drives

.
there's no OPTION for formatting XP drive & then re-installing, ONLY TWO Options-
1. Standard Recovery - no file (ur personal) is affected.
2. Full System Recovery - HDD is completely Formatted, thus you'll lose all partitions.