it's happened to me a few times too. Speed isn't the issue. It's just got a few bugs...
A faster processor would help. My editing system is dual, dual core Xeon 3.0ghz processors and I rarely if ever have a problem.
Other issues to consider is the type of video, HDV is very intensive, large scale images (over 2 megapixel) can also cause problems, and projects over 30 minutes can also bog down a slow system like yours.