On an XP computer, right-click "my computer" and click on properties. Select the "computer name" tab and note the workgroup name. On your windows 7 computer change your workgroup to match the name you noted on the XP computer.
Also, on the right most image you sent, highlight Internet protocol (TCP/IPv4), then click on properties. Make sure "obtain an IP address automatically" and "obtain DNS automatically" are selected.
Awesome. I appreciate the response, but now I've run into another small problem.
I'm connected and can see/access the other computers, but when they click on mine, there aren't any folders. How do I go about enabling sharing through my computer? It seems like it'd be simple enough, but I can't seem to find it with Google.