Here are the first few things that spring to mind:
Have you installed the After Effects CS4 (9.0.3) update? That update fixes a lot of problems.
Are you using OpenGL? If so, don't. See this document.
If you have Aero enabled in Windows 7, turn it off.
Try without the audio file that you added right before the problem arose. Try without Sure Target. Make sure that you have the msot current version of Sure Target.
I am running the 126.96.36.199 version
I have unchecked 'Enable OpenGL' on the Preview page of the Preferences.
I have disabled the all the Aero functionality I was able to locate.
Will restart AE and report back.
Thank you for such a fast response.
No clue what caused the issue, but after adjusting the things above, I tried clicking through multiple projects and the only one that was STILL giving me issues was my current one.
Others involving full resolution HDV footage were fine, so I did a screen grab to remember my Sure Target settings, and then deleted it out of the comp and now I can scrub through it and click options and it doesn't crash.
Prior to cleaning up these other issues, it wasn't working in any project but following your advice, it appears I can get back to work. Thank you for your help! I'll for sure be back here to learn but hopefully not have to ask any more questions!