Mac Book Pro keeps freezing up.

I have a 2.16Ghz MBP with 3GB of RAM. I have had it a few months now with no problems. Recently the computer has begun to freeze up on me. One time it was the entire computer and I had to take the battery out. But the majority of the time it is just the application I am currently running (if I'm running more than one its the most fore-front application presently in use). The little colored spinning wheel pops up and the fans start running full speed (so the computer gets really loud). I'm assuming this is because it's working really hard to fix the problem and overheating? Well, it's never able to fix the problem and I always have to force quit the application. While it isn't the end of the world to have to force quit an application, I thought that was a more frequent thing for PC's, not Mac's, and it's a bit of a pain especially when you haven't save your work.
I downloaded a bunch of software for school, and switched my Safari to enable Rosetta right before all of this started happening (though safari is the most common application to freeze, it's not the only one). Could one of those things have something to do with it? In addition to the freezing (which can happen on any of my applications), safari sometimes force quits itself, just shuts down and closes completely for seemingly no reason. I've run a full virus scan and my computer is completely clean. Any ideas??? Thanks in advanced,
Michael

Why have you enabled Rosetta for Safari? There shouldn't be any need for that. Note: a virus scan will not help you diagnose a problem on your Mac. There are NO viruses that affect Mac OS X; not yet, at least.

I enabled Rosetta for Safari because I was instructed to by one of my professors. Enabling Rosetta for Safari is the only way I can few certain online virtual classroom sites. Note: I have a Mac specific virus scan. There are a few out there that affect Mac OSX, not many, but a few. Could the Rosetta be causing my problem? Any other ideas? Thanks,