What model printer do you have, and what flavor of Unix are you using? I support Sco Unix (and also Redhat Linux) POS systems, but all of the printers we have out there are a bunch of old Lexmark dot-matrix and a few new Lexmark lasers, and all have parallel connections. So I haven't actually dealt with a USB printer under Unix, but...I'm running SuSE Linux 9.1 on my machines here at the house. I've gone without a printer for years, since I don't have Windows, and it's quite difficult to find one (especially an inexpensive one!) that will work outside of Windows. I was at Wal-Mart sometime in the summer and they had a cheapo Lexmark Z25 USB printer there for like thirty bucks. I saw a penguin on the side of the box next to the Windows and Mac logos, so I figured I would give it a shot. Downloaded the Linux drivers from their site, but their installer would crap out when trying to run it. Had to do a bit of googling, reading, and tweaking to get the drivers to install, but in the end, it works great. I have it hooked to the box in the bedroom, and can print to it through CUPS on my other desktop and laptop. So, it is possible to get one of those beasts working... Just depends on whether the manufacturer was kind enough to release non-Windows drivers for it, or if they at least let folks know how the printer works. More often than not, USB printers tend to use some sort of proprietary language and whatnot, which can cause these things to become a big paperweight when you try to hook them up to anything other than a Windows box. This site doesn't have much about Unix, but does have plenty of information about what printers will work in Linux. You may find something usueful here, I dunno...
http://www.linuxprinting.org/Good luck to ya! If you have the right printer, I'm sure you could get it working...