Doesn't address the issues, but speaking purely financial: (Not trying to be snarky,) but perhaps you should familiarize yourself with 30-day free trials?
ATI Radeon as your graphics adapter?
Try updating the drivers from ATI's web site.
If you search the forums, there have been other Mac users that have had crashes when moving clips around the timeline. Being a PC guy, I don't remember if they got it solved or not. But it's worth a look anyway.
Make sure all hardware drivers are up to date. Also there really is no need for Cineform with CS5.
A great starting point would be to list all of your hardware in detail. Next, give us the specs. of the Assets (source footage) that you are using, and the Sequence Preset, that you have established. This ARTICLE will give you tips.