Since we have no idea what is on your startup drive or how big it is in the first place, this is almost an impossible question to answer. Stripping out unused printer drivers has already been suggested. Add t that, running
Monolingual and ditching any unneeded language localization files will yield you a net gain of a few, very few, MegaBytes, but certainly not not GigaBytes.
Run
Cocktail or
Onyx to clean up the log files, archived logs, and cache files and you will probably gain a whole
lot more disk space than deleting unneeded language localization files and print drivers. Just remember this is a temporary gain and you will have to repeat this step periodically to stay ahead of the accumulation.
WhatSize is a handy freeware utility that will scan all your visible and invisible files and folders and rank them by size so you at least know where your disk space is going. Be careful with any utility of this type because it will let you delete almost any file on the system and used injudiciously can quickly render OS X inoperative and unrecoverable.
Among the user's files, music, photo, and video files can eat MegaBytes of disk space in nothing flat. Then your only choice is which are you willing to delete. Just remember you can delete a song in iTunes and unless you specify that you also want the file deleted it is still taking up the same amount of disk space.
Warning: any time the free space on your hard drive falls below 15% there is a greatly increased risk of irreparable damage to your file system occurring, so you probably need to clean out a lot more disk space than you think you do to get below the 15% free space level. It may be time for you to consider:
- Replacing your hard drive with a substantially larger one
- Adding a second internal hard drive to your system if possible
- Adding an external firewire hard drive to your system
- all of the above
Finally the problem may be the file system is already damaged and yielding a false report. Boot from the install CD or another bootable volume and run Disk Utility > Repair Disk and see if any problems are detected. If problems are found and repaired, rerun Disk Utility until no more errors are found or Disk Utility reports irreparable errors. If that happens try
TechTool Pro 4 or
Diskwarrior 3.
Good Luck!