it sounds like you are new to the computer, so i might reset the preference file an see where that get you.
hold command+option+shift while starting up ae to reset the preferences to the default settings, and then see if ae doesn't run better.
after that i'd look at the relative information that todd kopriva lists here (in particular the recommended ram settings):
http://forums.adobe.com/thread/543440
Kevin Camp
Senior Designer
KCPQ, KMYQ & KRCW