Do you mean Pocket PC or Win CE? How far back do you want to go?
All recent PocketPCs will have a generic IR modem in the list, use this it should work fine.
Windows CE was also supported by the old DI27/DI28 infra red snap-ons available from Ericsson. Try using their support website. I can definitely see the driver there for the DI27. The address is
mobileinternet.ericsson.com
You will need to register to download anything. Or you could try this
link