A mere 2 gigs of memory is barely enough to run the OS and couple of simple applications, to say nothing of running After Effects, the ultimate memory hog. You need more RAM. Fill that machine up with memory!
And since you don't say if you have EVER used AE before, go look in AE 9's online help on this web site, and search for the term "preferences":
You'll want to delete AE preferences, and you can do so by deleting a text file. You need to know where it's located. It might help you get AE started.
And if you are indeed a newcomer, you should also look at this: