Hook only the host up to the dial-up modem. If your
having problems ICS (Internet Connection Sharing) may not
be enabled. To fix this run the Network Setup Wizard on
both your machines and follow the on-screen instructions.

(Network Wizard = Control Panel>Network Connections> on
your left under Network Tasks run the Set up a home or
small office network. [Make sure you dont change any
settings but which computer you use to connect to the
internet with.]) Its pretty user-friendly so just read
everything.

Hope i Helped,
~ Mitch