What O/S are you using on each computer? I've gotten it to work just fine (using a MN-500 also) with Win98 on both machines, XP on the wireless and 98 on the wired, and XP on both machines.
As of now (with XP on both) I just right click the printer and hit Sharing, give it a name. It doesn't show up under My Network Places but if I click Workgroup Computers and go into the computer its wired into, it shows up. (And if I try to print something on the wireless computer it shows up as well)
IIRC, it took more setup when the wireless one was using 98. Despite it being shared on the wired computer, on the wireless computer I had to manually setup the connection. (I forgot how exactly but if that computer still had 98 I could do it)
(Sorry if this isn't much help)