Do I need to worry about wvdial and/or other dial-up ppp connection messing with the broadband Ethernet setup?
That should not be a problem.
Could someone point me at the URLs of the other 'dialup' related documents that are supposed to be in the Arch Linux Wiki (since searching for 'dialup' didn't help me)?
Well, I haven't succeeded in doing this, and it is the only thing keeping me from ditching OSX on my macbook, but it should be possible to use netcfg for this. So it should just be a matter of disconnecting your ethernet-profile and connecting to your dialup-profile. The forums have a few solutions, but neither has worked for me. Mind you: I am trying to connect to my BT smartphone, and use that as a dialup-modem. Your setup should be easier. Zl.