RunDLL32.exe processes are 500MB & slowdown

We have a Toshiba SATELLITE U300-13-N notebook with this hardware:
System

Two Rundll32.exe-s come up during mornings at arbitrary times - also at every restart - , possibly after closing internet explorer, consuming all RAM & slowing down the Notebook to a crawl.

RunDLL32.exe 512MB

Originally same problem was under Vista 32-bit with an old Norton 360. We upgraded to Windows 7, then run the Norton Power Eraser: above problem persist. Followed instructions described in this thread. Run a quick scan after upgrading to latest Norton 360: 3 cookies, but no dice.  Plan to do full scan in safe mode this afternoon. 

Tried purchased Kaspersky boot CD scan, Tried purchased Panda, Bitdefender Trial, Webroot trial, Malware removal tool. Hijack This gives a lot of entries, because my boss doesn't want a HDD reformat. All data must remain intact.

Now what?