I finally got my Canon iP1600 printer that's connected to my Server 2003 x86 machine via USB to work from my Server 2008 x64 machine and wanted to note how I did this in case I need to do it again in the future.
From Canon's PIXMA iP1600 page select the Drivers & Downloads tab. From the OS drop down select Windows XP (x64). Install driver with filename ip1600x64190dej.exe
Now find the printer on the network and add as printer.
Before doing the above I'd selected the Windows Vista x64 OS and had installed the Add-on Module for Printer Driver (aomvstea23us.exe) but I don't believe that this was neccessary.