Printer Sharing--Vista and ME

Hi All,

I just got an HP all-in-one, model C5180. The AIO is connected via Ethernet
cable to my Buffalo Air Station router. My Windows ME PC is also connected
to the router via Ethernet cable. A laptop running Windows Vista Home
Premium connects to the router wirelessly.

I installed the C5180 onto the laptop last night...no problems after
downloading the Vista stuff from HP's site. It made a couple of prints OK.
Today, I tried to install the C5180 on the Windows ME machine. It could not
locate the AIO. The C5180 is "on," and I tried letting the installation find
it automatically, and also by typing in the MAC address, hostname and IP
address. It just won't find the AIO.

Why would the Vista laptop be able to "see" the printer so easily with a
wireless connection, but the ME machine can't see it even though they're
both on the wired "side" of the router?

Got any ideas? Thanks in advance.