What's going on with the space on my harddrive? URGENT!

Along the lines of my question yesterday, I’m working on a document in Pages (Apple’s Word-like program), and it has many images in it and thus is about 50MB. My computer has about 2GB of free space (I know, I know, there should be more, but I DON’T have time to deal with that right now).

I empty trash and restart my computer, I’ve got just over 2GB. I open my doc, and the few others I need open while working on it (just regular documents), and it stays the same. After a few minutes, my free space goes down to 1.17GB. Kinda weird, but no big deal since I can still work. But within 15 minutes it’s down to 600MB, then 300, next thing you know I have the dreaded “Zero KB” popping up and I can’t even save. If I quit Pages before it gets to that point, it goes back to 1.12GB.

Clearly this pattern is happening over and over again, with slight variation.

What the heck is going on? I know the free space fluctuates for various reasons, but this is MUCH faster than it was before last night (which is when I started this big document). I don’t see anything in Preferences, and having to quit and reboot frequently is just not an option – my Master’s Thesis is due in less than 12 hours!! Please help!