Help! Can't use my Mac Pro!

I have a Mac Pro 2006 1.1 with a 250Gb hard drive. This worked for a long while, then developed a fault and went really unstable. I think this is because the hard drive is nearly full. The operating system will load and if I'm lucky will do simple tasks before hanging, but almost anything I need to do causes it to hang. This includes transferring stuff to the bin and trying to empty the bin. So I haven't figured how to get this hard drive working.

Alternatives:
1. I tried to load Tiger from...

Help! Can't use my Mac Pro!