Actually, most APPs don't take up that much space, GarageBand does though with all it's stuff.
In 10.5.8 my 226 Applications & 161 Utilities use 23.87 GB of Disk space, that's about 6 DVD sized movies.
How much free space is on the HD, where has all the space gone?
OmniDiskSweeper is likely the easiest/best, and is now free...
And if needed, you can use Terminal to run it in admin mode to see files/folders your user can't see...
Monolingua can remove unused languages, Printer Drivers & such, but use with caution on other things it can do.l...
Just asking... have you emptied the trash lately? Space of trashed items won't be returned to the Disk until you do
If you have all your data backd up, you could erase the Disk & reinstall, but I think the above things are beter way.