ok, if you have a default gateway, then try pinging from all of the computers separately:
1.) go to start menu
2.) go to run
3.) type cmd
4.) type ping http://www.google.com
What that will do, is 1. see if you're resolving to a DNS server, and 2. it will test your internet connection. If you are connected to the network but it says that you have limited or no connectivity it sounds like you might have a problem with your wep key. Make sure that the laptops that are having trouble connecting are using the proper wep security, and the right passkey. Post the results of the ping please.