I am having a bit of an issue getting NAT to work on a windows 7 guest. I have Ubuntu 12.10 and virtual-box 4.1.18. I have guest additions installed and working within the windows 7 guest. Bridge works occasionally but it is having issues as well. The problem is I need NAT to work because the Guest Network at my work allows employee owned devices to be hooked up to it and I believe that is why the windows 7 guest is not connecting to the internet because I have to provide credentials when logging in with Ubuntu.