I have had this problem. I installed windows 7 on my shuttle PC and i couldnt connect it to my router at all. i just got the red X.anyway. I tried all i could to connect it (installed XP/Vista 32/64-bit drivers on it) and a few more drivers i found and it still said under device manager that my Ethernet controller was not installed. Anyway, im pretty sure that this whole "not connecting with the ethernet controller" thing has to be a windows 7 error.
My solution to this problem is to just install a PCI Ethernet Conroller card. I stuck mine in and it worked perfectly, and i didnt even install the driver for it. So please send microsoft your feedback about it and hopefully it will be fixed when the real Windows 7 comes out. Hope this...