wow, you're using old hardware and old software.
What format are your sources and what are your sequence settings?
You may have a corrupt sequence, a corrupt piece of media, an incompatible format...
First step is to delete your fcp preferences. You'll need to do some serious googling to find out how to do this. Don't think digital rebellion's preference manager will work, but might be worth a shot.
If you have a corrupt or problematic piece of media, try rendering sections of the sequence til you find the problem. Probably around 83% into your sequence.
Here are a bunch of troubleshooting steps, some of which may apply to your configuration.