It was totally IE8 on my system. I only run NOd32 in real time and never have a problem with speed. As soon as I put IE8 on everything slowed to a crawl (web pages loading, applications starting, etc). Once I went back to IE7 everything was fine again.
I actually like IE7 (have it set up for the kids with their favorites, etc.) with the pro add on, its just that I like firefox better (due to a few specific addons like webmail notifier. I like opera too (its the snappiest on my machine for sure), but since it doesnt have a few features that I like in firefox i don't use it much.
There is definately some sort of snag in IE8 that affects some of our PC's. Just like all other software out there, it just doesn't seem to affect everyone's the same.