I finally figured out how to print to my unsupported HP T45 Officejet which is connected to my Windows 2000 server via parallel port. This will probably also work for other HP deskjets and other versions of Windows provided they are hooked up similarly.
Since I didn't want to spend money on a print server to make my T45 a network printer (and lose the scan/fax abilities by not being connected to the printer port), I downloaded a program for Windows called WinLPR 3.0 (40 day free trial, $25 purchase) from Alixoft. This software will allow you to send print jobs via TCP/IP (IP address) to your printer hanging off a parallel port (don't know about USB). After installing and configuring the software (pretty easy) and printing a test page from WinLPR, I switched back to my Mac.
Next I downloaded and installed gimp-print for OS X. This installs several HP deskjet drivers, Included are the 895c and the 850 servies driver, which are compatible with my T45 Officejet.
Next I setup a new printer in the Print Center. I clicked Add Printer, selected IP Printing, typed my Windows 2000 server's IP address and checked "Use default queue on server". Then I selected Printer Model "HP" and located the compatible drivers (pcl-model#) for my printer and selected "Add". Depending on your printer and if you have the latest drivers from HP, may have to select a printer driver from the "ESP" list under Printer Model. You may have to experiment (and run lots of paper through your printer) until you find a driver that works. I just now added a LaserJet 6P the same way at work, so it will work for some LaserJets too.
Now I can print to my T45 Officejet. The quality is OK, and I can print from MS Office and IE just fine. I can't print from Adobe Photoshop, but I have a separate Canon Photo printer and use it primarily with Photoshop.

