2) see if anyone can help me find the registry edits needed to enalbe Profile loading logging. I simply cannot find this anywhere after looking for about an hour.
I think what you want is called userenv debug logging - details on the MS web site
it feels like a server problem unless you've perhaps made some change to all the workstations (permissions tightened on c:\documents and settings? - unlikely because that would mean user X would never log on)
Dodgy network cabling or switch? Can you run wireshark? What you're looking for is excess traffic (and for this you really need to know what "normal" looks like; loopbacks on a switch can cause symptoms like this and you'll see masses of traffic. Lots of it is "normal" but just retrying and retrying)
Failing disc on the server? Anything logged in event viewer or disc management tools?
Run performance monitor on the server - what does the disc queue look like (should be <1 for normal working; anything more suggests the disc is stressed; then need to find what is causing that stress)