Best solution? Put a Wi-Fi card in your computer, then connect to a desktop system in your house running Internet connection sharing. (You'll also need a Wi-Fi card in the desktop system.) Or take the PC that uses the modem and dialup connection and add to it a wireless access point and Internet connection sharing.
If you have the bucks, you can get a Wi-Fi base station with a built-in modem, such as the Apple AirPort. It has a built-in modem right alongside the Ethernet port.
