Assuming you've got precious data on your Mac, I would say you should start by backing up the data. If it's a relatively small amount of data that you need to backup, you can simply burn it on a blank CD/DVD. Or if you have a network, you can back it up on another machine.
Now that you're ready to wipe everything, I would suggest the best thing to do is follow my guide to reinstalling Tiger. Make sure you choose the "Erase+Install" option when installing, and it will automatically reformat your hard drive.
http://www.daniweb.com/techtalkforums/thread54207.html
Hope this helps
John A
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After moving items to your trash, you have to empty the trash bin before the items will be deleted off of hte drive and space recovered.
cscgal
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Try using Disk Inventory X. Download it from here: http://www.derlien.com/ . It shows a map of your hard-drive with colors for kinds of files. Check it out. You probably have some 1GB movies out there. Compress them with iMovie
Lomoco
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