hi mel,
take a look at the properties for c: drive,
not sure about vista (don't have it) but
the indexing function is turned on in xp and earlier.
here is a nice utility (microsoft purchased the company)
from sysinternals, autoruns
it shows you all the stuff that takes off on autopilot
when you startup windows. you can turn them off
with a mouse click (no need to edit the registry yourself)
lot of software is setup to 'call its mother' and check for updates, this can be a reason for your disc activity.
http://www.microsoft.com/technet/sysinternals/systeminformation/autoruns.mspx73 james