|Is it another HDD or another partition on the same HDD? If it's the same HDD, how about merging partitions? Or just expanding a little into the 2nd one?|
Try this 1st:
Start by going thru all your files, folders & programs...delete or install anything you're sure is unnecessary. And don't use your recycle bin for storage. Delete it, make sure you don't need it, then empty it.
I'm not a big fan of System Restore & keep it disabled on my systems, but if you prefer to keep it enabled, consider lowering the percentage of HDD space it uses. I believe the default is 10 or 12%, so that would be approx 3.0 - 3.6GB out of your 30GB. I've read that the average XP restore point is approx 25MB, so at 3.0GB space, that's 120 restore points. Now ask yourself this: if I were to have a problem where running System Restore was necessary, how far back would I need to go? You can reclaim all the wasted space by lowering the percentage to something more realistic. If you decide to do it, immediately create a new restore point afterwards.
If you don't have a cleaning program, install & run CCleaner-Slim. If you're the type that likes to store your passwords so that you don't have to log in to sites all the time, uncheck the box next to 'cookies' before running the program. I always uncheck the box next to Recycle Bin & empty it myself as I see fit, but that's up to you. Run the program, delete everything it finds.
After doing all the above, see how much free space you gained.
EDIT: I just noticed you're running Vista...that kind of kills the restore theory. Vista's restore points are MUCH larger than XP's...a single point can be 1GB or more.