trying to install autodesk 3.3 on work computer. they gave me the cd with the serial # and it keeps coming up 'invalid serial number'? any suggestions???? thanks!

Questions about serial numbers, invoice number, authorization codes, etc. are better to be discussed with your Autodesk dealer. Other peers cannot help you much getting your purchased serial number.

What exactly is Autodesk 3.3? What program are you installing?
 
I had a similar problem recently when installing Autocad 2011. A simple email to Autodesk cleared up the issue.