I am also running Mac 0S 10.6 with the HP3100. When I have encountered this problem of not being able to retrieve the paper list, I've resorted to deleting the printer from the printer list in HP Utility, restarting the computer, and re-adding the printer. If I remember correctly, I also did this with the Print and Fax window in System Preferences -- that is, I deleted the printer and then re-added it after restarting the compute.
I have no idea why this works, but it has for me (so far).
Good luck!
David V. Ward, Ph. D.
www.dvward.comDavid V. Ward Fine Art Photography