It's very easy and in fact I'm working through this kind of setup right now, though I'm using Win7 desktop connected to a WinXP netbook.
1) Connect your PC to your laptop via the Ethernet (LAN) cable and change the type of the established connection to "Home Network" in Network and Sharing Center (available both in Vista and 7) on both machines.
2) Switch on the Wi-Fi on your laptop and connect to your wireless network.
3) On your laptop:
a) Open Network Connections by clicking the Start button Picture of the Start button, clicking Control Panel, clicking Network and Internet, clicking Network and Sharing Center, and then clicking Manage network connections.
b) Right-click the connection that you want to share, and then click Properties. Administrator permission required. If you are prompted for an administrator password or confirmation, type the password or provide confirmation.
c) Click the Sharing tab, and then select the Allow other network users to connect through this computer’s Internet connection check box.
4) You should be able to connect to the Internet from your desktop now.
Copycatted from Microsoft ICS article found by Google in 5 seconds. Good luck with the ICS, don't be afraid to search and try out things and...
... for hell's sake, cut the caps. They don't help.