The newest version for Fedora distribution (Fedora 14) has a bug on NetworkManager using DHCP that prevents your network settings from acquiring a default gateway.
This won't allow network requests to go outside your local network.
There is an annoying workaround that requires you to use your console, su to root, and type:
route add default gw aaa.bbb.ccc.ddd
where aaa.bbb.ccc.ddd is the IP address for your gateway (typically your router).
This bug is already reported.