Yes, you can have multiple concurrent network connections with no problem in OS X, wireless included.
However, if more than one provides internet access, all of your internet traffic will default to the connection highest up in your System Preferences > Network > Network Port Configurations panel.
So yes, you can use an AE base station to control your music, while using another router for internet access.
If you're afraid of ppl highjacking your stereo, i think there's a password option for outputting to a certain AE audio output. And of course, you should always secure your base station using the many techniques you'll probably find in the Networking forum.
Which is where this thread will probably wind up
