My company recently upgraded to 2005 due to 2000LT causing AutoCad to lock up during printing.
2005 cured that problem but was incredibly slow. An associate found the way to fix it after several weeks of annoyance.
Right click the AutoCad icon and then left click Enable/Disable Digital Signature Icon. Click the check box to clear it and it doubles the speed. Apparently it was looking through every drawing for a digital signature and that was what was causing it to be so slow.
Hope this helps anyone who has the same problem.