I'm in the process of getting my broadcom wireless card on my Acer laptop running in fc5. Right now, I'm in the middle of using the the bcm43xx driver and NetworkManager. It's turning the light on and, most recently, on boot up, supposedly given me an ip address.

However, once everythign is actually up and running, it won't connect, although NetworkManager shows the AP in its menu. That wouldn't be a big deal except that the wireless is only set-up as a local LAN--I use dial-up to connect to the internet and now, when I dial in with wvdial, while it says I've got an ip, my web browser won't connect and I can't ping a www server.

It's somewhat reminsicent of when I first got the modem working--for reasons I still don't understand, I had to specify particular DNS servers to use, which allowed me to actually get on the web, despite wvdial claiming I had an ip.

I'm GUESSING what's happening is that Linux is looking for the internet on the (unconnected, and not quite working) wireless connection, and not via the dial-up. But I'm totally clueless about what to do about it....Any suggestions?

You need your service providers DNS address/addresses in the file /etc/resolv.conf.
Even if you are using dhcp and having difficulties browsing etc, it is a good idea to have them setup.
With ipforward, computers on your lan, I am presuming with fixed ip address's, will also need DNS entries in their /etc/resolv.conf. If you have a windows computer on the lan set up the ip manually with DNS entries.
There are good tutorials on DNS on the web, but first of course you need to be browsing.
If the installation of your wireless card overrides the DNS eentries in resolv.conf, set the card up manually with a static IP. This is the most convenient way if you are having problems connecting.
Hope this helps.