XP 100% CPU on Login, by random processes

Solution 1:

Sounds to me (from your mention of NetMeter or TaskbarShuffle) that you might have a lot of add-ons, toolbars or other evil little whatnots installed that are playing tango for your CPU following a startup. Use something like SysInternals Autoruns to identify what's happening when you start up, and selectively disable until things return to normal.

This may also be AV software at work. I've seen recent versions of AVG, for example, consuming 100% CPU for about 5 minutes following a cold startup. And speaking of AV, you definitely shouldn't discount a virus.

And yeah, this is really more appropriate for SU.

Solution 2:

http://blogs.technet.com/markrussinovich/archive/2010/01/13/3305263.aspx

The case of the slow logons.. fascinating article btw.

Basically, he logs the entire boot with process monitor and checks for large gaps.