Wi-Fi & Dialup networks don't play well together

I live in an RV, which makes it difficult to run cables around. I have an HP
laptop with Vista Home premium, an HP all-in-one with wi-fi built in, and an
AirCard which connects me to the Internet via Cell Phone towers.

Everything works fine--but not together. I can log onto the Wi-Fi network
and use the printer/scanner. I can log onto the EDGE network through the
AirCard and reach the Internet. However, I can't log onto both at the same
time (meaning I can't print out an Internet page).

In fact, if I've been using the Wi-Fi network to print something then decide
to go on the Internet I must not just reboot, but actually shut down the
system, switch the (Linksys W54G) router off, unplug and reinsert the
AirCard, then restart, and log onto the Wi-Fi network to reach the printer.

The same is true the other way. If I've been on the Internet, I must shut
down, unplug/replug, restart, log in, etc., etc. in order to print anything.

I pressed the Diagnose button and Vista reported that the problem was I was
logged into two networks, and suggested I shut one down and see if the other
worked.

Does this mean that Vista can't handle these two networks at once? If so,
can Vista Ultimate? Or what?

Thanks for any help,

Al