Hey FX
Your pro is now using 8 cores - WOO HOO!
To the people who were all worried about power supplies and such - you are not well versed on the subject. 4-8 core upgrades have been done on Mac Pro 1.1's for a long time.
If you want your processors properly recognized and some fine tuning for your fan speed, you need to look up 'Mac Pro 2.1 Firmware tool'.
You can read a good thread, and probably a download, here.
http://forum.netkas.org/index.php/topic,1094.0.html
You will need an internet connection. The package is a script that downloads and installs the appropriate files. I (and many others) have done this and all works quite well.
Cheers, AJ