Without knowing which printer you have, or any other information, I would have to say that the chances are slim to nil of sharing a printer across the two OS's. Even sharing within OS X is not happening at the moment. This might be something that is taken care of with the next release of OS X, but don't hold your breath. Many printers allow sharing from OS 9.x, but not OS X.
Have you attempted to connect to the printer after sharing it under OS 9.x?? Which version of 9 are you running??
As for using an USB to ADB adapter, you will have to make sure there are drivers for it for OS X before even attempting it. Since you have an old printer (any without USB ARE old, since that has shipped on printers for more then a couple of years now), I would suggest getting a new one instead of d*cking around with the old one. If you want to have just one printer, get the Epson C80N, and set it up on a LAN. I have such a printer and can print to it from OS 9, OS X, and win2k without any problem at all. OS X has the least trouble of all of them for using it. The inks are very nice on the C80, since they are color fast for ~70 years, water proof, and are in their own cartridges (so that you don't loose ink when one color runs out, but the others still have some left). The cartridges also have memory chips on them to give the ink level even if you remove the cartridge and install a different one. You put the old one back, and you get an accurate ink level.
All in all, the printer is worth the money.
