Connecting a XP and VISTA computers

Hello,
I have a big problem that i cant seem to fix. I would like to form a simple connection to two home computers giving both internet access.

I have the main computer which is connected to a speed touch modem via a usb cable. The main computer is in Windows Vista.

The laptop used to connect to the main computer by ethernet cable and be able to use this interent.

Since installing WINDOWS VISTA on the main computer i cannot seem to be able to set up a connection. All i really am after is that the laptop has an internet connection.

Really need help urgently if this is possible as both users have uni exams to study for.

Thanks!