what is taking up hard drive space?

hello.

I have a power mac (pre intel) quad core desktop running 10.5.8.

I have noticed it being very sluggish lately.

From taking 5 minutes to boot up, to browsers taking longer to launch(with the color wheel spinning longer until the browser is fully ready), to inputing text into fields in a browser window(the text gets entered a second or two after typing). Even when I open a finder window, the icons for every file, as well as the size listing of each file/folder will take like 10 seconds to start loading one at a time. I never noticed that before.

So I opened disk utility, and noticed that I have filled up 160GB out of the 233GB that this hard drive has. That seemed like a really high number.

So I added up the total size of the home folders in all 4 users on this computer, and they add up to 27GB. The system folder is 4 gigs, and the main Library folder at the top level is 51 gigs. I don't think there is anything left. That adds up to 82GBs. Where is the other 78GBs coming from?

I know I'm missing something, but I can't figure out what.

Even still, I don't know that this is the reason for my computer to act sluggish, but now I'm curious how I'm filling up so much hard drive space.

Any thoughts on finding this info out, and/or fixing the sluggish issue?

Thanks!!