When installing a new printer earlier, I first installed it in Windows Server 2008 R2 (which of course only exists in a x64 version), and tried to add the x86 (XP) driver since all the clients run XP.
After providing the “additional drivers”-wizard with the printer driver, it asked me to “Please provide path to Windows media (x86 processor)”, which was a bit difficult since I had no 32-bit media (I would have tried 2008 32bit or similar, if so).
Turns out, the solution is blindingly simple: Share the printer, and with an admin user (typically the same who installed the printer on the server), log on to an XP computer, and install the shared printer from there. It will ask you to provide the driver since the server has none. After installing, go into printer properties in XP, find Sharing, Additional drivers…, and check off “Windows XP/2000, x86″. The driver will be uploaded to the server.