I have a dual xeon with 2 gigs, and AE was slow about the same as you posted turns out my problem was way too many fonts I had 7000 of them, I bought a program from extensis called suitcase which allows you to make them invisible to windows until you turn them on when needed. you can turn fonts on individualy or a bunch at a time, hope this helps.
Luc
Cygnus Video Productions
LV,NV