I have att broadband too. To get it running I had to use windows (really unhappy about that considering I had recently reinstalled Redhat with no window partition!). So I re-re-installed and put windows on a small partion so that I could use their install disk. I then had to use windows to get the dns numbers, the techs said they couldn't provide them for me. Unfortunatley I can't remember how I did it at the dos prompt.
As for as your ethernet card is concerned, it may have already been configured in your kernel. Once you get the internet connection on windows going, go into linux and see if it's there. If you can ping your dns numbers you're on. If you can't, you may have to compile your kernel with the appropriate ethernet card modules.
There may be a way to get the connection to your place without going through windows, but I couldn't tell you how. Good luck.