Thanks for your responses, guys.
I downloaded the installation manual from Seagate and the configuration notes indicate that it should be off and if the drive doesn't load then the cpu's motherboard needs the jumper to be present. I've used this drive for a year in a firewire enclosure as my local network Time Machine drive with no trouble. When I put it in the MacPro it started to act flakey and it would take Disk Utility 15 minutes to repair it - repeatedly. That's why I started wondering if the jumper should be on. At this point, it seems clear the drive is going bad.
Thanks again for the kind replies.
-Russ