Assuming that the main PC has the dial-up connection, there are two things you need:
1. Connection between the notebook and PC either by a cross-over ethernet cable or through a wireless router.
2. Internet connection sharing enabled on the main PC.
To connect by wireless to your notebook, connect a wireless router by an ethernet cable to the main PC's network card. Note that wireless routers typically have one port labeled for an internet connection such as a DSL high-speed connection, and perhaps four other ports - use on of these other ports to connect to the main PC.
The wireless router must be compatible with the wireless band used on your notebook, for example wireless G.
Follow the router's instructions for the wireless setup, or use the Network Neighborhood 'Setup a Wireless network ..' wizard, but remember that your internet connection will come from the main PC and not from high-speed/broadband connected to the wireless router.
Once the wireless and 'Router to main PC' components are setup and you can see the main PC in the Network Neighborhood on the Notebook, then setup Internet connection sharing.
On the main PC run the 'Setup a home or business network' wizard from the Network Neighborhood window. Select the 'Share my Internet connection' option and follow the steps in the wizard.
The internet connection sharing system includes an option for the remote PC - your notebook in this case - to tell the main PC to make the dial-up connection or to disconnect from the phone line.