I don't know anything about Mac's, but on Windows you can reset your computer back to a time before your update when it was working fine. I hope it could be that simple, but it wasn't in my case. I had the trial version before I bought the CS4 Suite, and trying to install it was a nightmare. I spent days on it, finally called tech and spent many days and hours working on it with them. After that much time and money, I was bitter for a while, but it was worth it in the long run. Cin
Create a new user account that has the privileges set to User can manage computer and see if the apps launch. If so, your old user account has been "polluted" by the Apple update (so its Apple's fault, after all). you may try to salvage it by using tools liek OnyX and doing a little housekeeping, but if that doesn't work, simply migrate to the new account.
Just as a side note; if you want to seriously use After Effects, you will want a lot more RAM. To take advantage of multi-core processing AE needs at least 2 Gb of RAM per core of your processor that AE is using. Here is Adobe's Todd Kopriva's post on it.