Since the beginning of January the (theoretically) fasted machine in my network,  a 2.2 Ghz P4, has been turning around units in 15-20 hours. It's running the graphical version under XP

This is as opposed  to a  4-5hr turnaround on another machine, the1.8 Ghz  P4  running the CLI).  It's slower even than the old 450Mhz P2!  I didn't worry at first because all the machines get the occasional big one, but *every* unit take the better part of a day now. 4-6 hours per unit was the norm until the end of the December.

No new software has been put on the machine, no specs have been altered, and in every other respect it appears to be working fast and efficiently.  Can anyone give me a clue about what might be happening?