I haven't read all the pages on this thread, so I don't know if this has already been mentioned, but if you are using a HP computer, you should uninstall HP ProtectTools (if it is currently installed) as we have experiensed serious slowdown on multiple machines in AutoCAD caused by this piece of software.
It slows tooltip and general response times to a degree that renders AutoCAD virtually useless in large drawings.
good point and it does help. Usually when i have heavy apps running i turn off my firewall and norton. i don't recommend this. kind of hard on a corporate computer but maybe befriend the it manager to give you admin rights