going from win2k pro to win xp pro: upgrade vs. clean install

i'm currently running windows 2000 professional SP4, and i
need to switch to windows XP professional.

the cheapest way to go about it would obviously be to
purchase the $199 upgrade. however, the obsessive-
compulsive side of me would prefer to format the drive and
install a fresh copy of windows xp pro. only problem is
that a new copy of windows xp pro costs $299.

i just don't like the idea of having all these residual
windows 2000 files on my hard drive. is that what would
happen if i upgraded? or does the upgrade do a good job
about getting rid of all the old windows 2000 system files?

thanks a lot.