Apparently, that can't be done from the SBS box itself.
Instead, log on to any 32 bit machine as a domain administrator, go to \\servername and the go to printers and faxes (don't go to the printer shares you see there - go to the folder where printers are stored). Highlight the printer you want to add the 32 bit driver for and choose file -> Server Properties. Click Drivers and then Add. It's pretty self explanatory from there.
More info here:
Another option - which I have found easier and more effective . . .
Log on to a workstation as an admin with the opposite type of OS (with a 64 bit OS, log on to a 32 bit workstation or with a 32 bit OS, log on to a 64 bit workstation).
Download the driver and install it on the network printer.
Go to the printer properties.
Go to the sharing tab and click on additional drivers.
Check the box for the appropriate type of OS and it will upload your newly installed drivers to the server.