Normally, you can't share USB printers via Mac OS X Server because the Print Server can only deal with Postscript printers. However, you can share USB printers normally via CUPS.
Set up your printer as normal (System Preferences » Print & Fax). Then, in Safari go to CUPS, which is usually at http://localhost:631. Click the Administration tab, then click the Share published printers connected to this system checkbox. Click Change Settings, and enter your admin username and password. Voila, plain old USB Printer Sharing works.
Note that you can't use Print Server to manage the printer, but who cares?
Mac OS X Hints
http://hints.macworld.com/article.php?story=20080324224027152