Sharing method of Modem Internet to Wifi

I had a hard time facing my problem upon how to share my USB modem internet connection through WiFi from my laptop.
I am using wireless – G broadband router. This modem has already set for configuration already. I want that my desktop computer to share the connection via WiFi, also my laptop.
I thought wireless connection can get easy access for WiFi laptop.
Can anyone help me how can I connect the broadcast?
