I don't know the main menu structure for the OS on the eeePC, so I can give only general instructions.
In the main menu, look for System, Internet, or Configuration. Then look for anything relating to configuring hardware or system services. There should be something there for configuring your network connection (in this case, your internet connection is your network connection). There may already be a file for your wireless card that just needs a bit of tweaking to make the connection.