It is probably caused by a program looking for updates or new versions.
Have a look at the Startup Tab in msconfig and the StartUp folder in Start, Programs, StartUp. Also check if Windows is looking for updates in Scheduled Tasks, or was it called Windows Update.
Then examine the Tools, Preferences, Options or similar wording in each of these programs for "look for updates daily" or similar.
If I remember correctly Liveupdate (Norton) does this. It will be there somewhere.