printer is not visible to windows pc

I have a printer connected to my ubuntu 10.04 desktop machine. It prints fine to the printer. I have tried to set up samba and printer shares to allow my other windows machines (2000 and xp pro) to print to this printer. It worked once but then shutting down the ubuntu machine stopped it working and I have not been able to get it working again. As far as I can see it is set up correctly. Where should I be looking for the problem. the windows machines just can't see the printer at all.