***Friend's PC, so I can't be really specific***:
Dell (Model#? aprox 1 year old).

XP Home SP2
(Dell's 'proprietory' version. Why the [pick your fav explitive] does Dell need a proprietory version of ANY OS with their own dll files and drivers on a separate CD with a separate install? )
Oops, sorry, I digressed!:o

IE 6.x
Firefox 1.5
Free ZoneAlarm 6.0.667 (I think)
Grisoft AVG Free 7.1.375
SB S&D 1.4.0.3
Ad-Aware SE Personal 6.2.0.236
Irfanview 3.9.8.0
Corel Suite 12 (from Dell)
Any other software Dell typically supplies

Updates done before all scans on all security apps, scans done aprox every 5 days.

If I use IE's Tools> Internet Options>
Delete Cookies>
Delete Files (including Offline Content)>
Clear History>
SB Secure Shredder works fine. But after a couple of hours of surfing, problem returns. Even left overnight (unplugged cable modem), no luck.

Any and all help will be appreciated!
Person solving the mystery will be considered to be an