I have similar experience with school PCs, apb. On certain days of the week, and only very very rarely , it's SHOCKING how fast Internet Explorer is (indeed, all of Windows just moves really really fast), but most of the time (these are 933 P3 systems) it takes 15 seconds to open an IE window. It's completely random, but 93% of the time the computers act like something is crushing them... the login window appears, flickers for a few seconds, stabilizes a bit, the buttons appear... you click a button and the button moves a few seconds later...
It's almost as if you're trying to run Mac OS 9 on a system with 16 MB of RAM and not using virtual memory. Oh, wait, I've already done that and it's faster than this crap.