I just installed Vista (so far so good!) but I read somewhere to make the partition something like 16 Gig. After installing it, I still had 4 or 5 Gig free... but now a few hours later with updates and whatnot... I only have 800MB free.

Am I in trouble?

I moved the TEMP files onto a second partition I use for the page file to try and save room.

16GB sounds VERY small to me, I would have said it needs to be about 40GB...

So... am I screwed? Should I just do a reformat and reinstall?

If you've only just setup your system and its not too much trouble to reformat I would do it now, it'll only get worse as you fill the hard drive.

I always make a small partition for the OS and a big partition for the rest of the drive, allowing me to do a reformat once a year or so to clean things up. But the partitions stay the same, that way I can move all necessary files to the big partition while I reformat the OS side. Its not straightforward nor reliable to change the size of partitions so you really should pick good sizes to begin with.

I have Vista Ultimate installed and have had it for a good few months, and my C drive now has about 30GB on it, though admittedly I install all my programs on that drive. Installing a new hard drive in a few days and I'll either make that a 40 or 50GB partition, haven't decided yet.

Read some benchmarks the other day about the harddrive I'll be getting (Barracuda 7200.11 500GB) which said that the first 100GB of the drive is the fastest, then the speed trails off a little across the rest of the drive. So your OS partition could be 100GB on the Barracuda, if you wanted it to be.

I completely agree that your OS partition should be as small as possible, but you also don't want to run out of room - it needs room to breathe. 16GB is far too small, seriously.

Home basic: 20GB HDD with 15GB free

Home premium - both require 40GB HDD with 15GB free
Ultimate