There is information on TechNet for how to do this: http://blogs.technet.com/sbs/archive/2009/02/13/how-to-add-32-bit-print-drivers-to-sbs-2008.aspx
However I could not get this method to work. So here are instructions which DO work
Log into a 32 bit client system as a local administrator. In this case I used XP. Not sure how different this will be in Vista.
Remove any instances of the type of printer you are adding. For example if you need to install HP LaserJet 4050 drivers on the server make sure you do not have any 4050 printers setup on the client. Also open the Print Server Properties on the client and ensure the 4050 driver is not installed.
Create a mapped printer to the server you would like to install the drivers on. You will be asked to install the drivers for the printer. This installs them locally on the client.
Open the printer’s properties and select the sharing tab. Then click on the additional drivers button at the bottom.
Then select the 2000/XP check box and click Ok. You will then be prompted to select the location for the drivers. Use the same path as you used to install them above.
This will copy the print drivers to the server.
If you need to install the same driver on more than one server you must repeat this entire process including removing the drivers from the client. Based on documentation this should not be necessary but I was not able to update a second server without removing them. When I tried to update the second server I received an error message “Windows could not locate suitable print drivers” when I tried to update the 2000/XP drivers from the sharing tab.