Okay, I tried to re-install again this morning. There was an option on the screens to keep original settings, or to reformat in one of 4 ways. Since I didn't understand what that meant at the time, I think I went with keep original settings, which apparently meant no-reformat (though it did delete all the applications, as far as I could tell).

This time around, things look good. >10GB free, though at the moment, I'm just running whatever came on the CDs (i.e., I have a fair amount of software to load). Which is enough space for everything I need, though I will still investigate swapping out the hard drive (thanks for the suggestion Braindrain, I do actually have a good friend here with his own IT "we do everything" company, so I'll see what he thinks).