Slow Computer Since starting a Final Cut project

Hi folks! First timer here.

I've been working on a project on Final Cut over the year, and the film gets bigger every month (it's a time lapse of the year, actually). As I complete more of the film, my computer gets slower and slower, even when Final Cut is not active, which is mostly. Photoshop, Safari, Chrome, iTunes, all are operating at a crawl. And it gets noticeably worse every time I edit, which is about once a month. In the beginning of the year I had a powerhouse computer, no problems at all. Now, it's a snail.

I have a Mac Pro, I've installed extra RAM in the past with much success. But do I really need to install more RAM? Or is there a way to reallocate all of that memory back to the rest of my computer when FCP is not open?

Also, I've had Final Cut on my computer and been making smaller projects over the years, so I feel like this has more to do with this particular project for some reason.

Any help would help! Thanks everyone.
Mr. Numberman

Are you keeping everything on your system drive? Put all your media and Libraries on a secondary (fast) drive. Be sure all drives have at least 15% of their total capacity left as free space. Running Disk Utility once week is a good idea, too. Disk Warrior once a month goes a long way to preventing problems. Also, in FCPX you may want to start trashing some of the render files.

When you close an application, it releases all of the RAM it was using, that's not an issue on a Mac, really.

What specific Mac do you have, how much RAM? OS X andFCPX versions?