I'm posting this because of my own experiences. Most of the posts here seem to be about Realtek wireless cards, but I'm speaking of the wired network cards.

You may find that these won't work under Linux unless you go into the BIOS and enable the "LAN boot" option. From what I've seen online, this has something to do with the fact that their firmware sometimes "turns off" the interface and waits for the OS to switch it back "on." If you enable the "LAN boot" feature in your BIOS, this forces the interface to remain live (otherwise, how could it boot??).

Don't know if this affects some of the wireless issues here, but this is something out of the ordinary that might get overlooked. If you have a Realtek NIC, and everything seems to be configured correctly but you still can't get Internet, look at this possibility.

-- Stephen