Be careful when deleting files. A lot of people have trashed their system when deleting things.
Place things in trash. Reboot & run your applications. Empty trash.
Go after large files that you have created & know what they are. Do not delete small files that are in a folder you do not know what the folder is for. Anything that is less than a megabyte is a small file these days.
Empty the trash. Space isn't reclaimed until you empty the trash in three places!
The trash can...
-- in the dock
-- for iPhoto
-- with Mail
"The simple, fast way to save disk space"
OmniDiskSweeper is now free!
This will give you a list of files and folders sorted by size. Go after things you know that are big.
These pages have some hints on freeing up space:
Buy an external firewire harddrive.
For a PPC computer, I recommend a firewire drive.
Has everything interface:
FireWire 800/400 + USB2, + eSATA 'Quad Interface'
save a little money interface:
FireWire 400 + USB 2.0
This web page lists both external harddrive types. You may need to scroll to the right to see both.
Buy a flash card.
Just to be technical, a few comments on previous posts.
1) You can run Leopard on a Mac <800 MHz, it just isn't supported by Apple and requires special installation methods you can easily find on the web. Some people have done it and seem satisfied, but you are running a system designed for a much newer machine on an older one and there's a performance hit. I would also question if it is even worth it. Leopard is now also so old that whatever you can run on it will still be out of date. To make any kind of jump to current versions of anything you need an Intel Mac which means a newer computer.
2) Yes, you are not supposed to move applications out of the Application folder on the boot drive. That said, I have many applications running off a secondary data partition. I'm not running anything high-end like Final Cut Pro but my browsers and a bunch of smaller applications seems to be content running off that partition. The same might not be true of newer system versions.