You will want to check the following:
1. Click "start"
2. Click "control Panel"
3. If not already in classic view, use the link on the left and switch to "classic view"
4. double click "network connections"
5. Find the connection named "Local area Connection" (may have a 2 or three after it) and right click on it.
6. select properties from the drop-down menu
7. Under "This connection uses the following", locate the one that says "internet protocol(TCP/IP)" and highlight it.
8. click the button below it that says "properties."
9. Make sure that both of the options on the properties window are set to "automatically detect."
This is the only thing I can think of, unless your bit-Defender has a built-in firewall. You might check the setting and make sure that your internet protocol port is not being blocked by the firewall. Also, If you do have a firewall running other than that built in to windows XP, you will need to be sure and disable XP's firewall, otherwise, they will be competing and block your connections.
Hope this helps,
feel free to email me if you still have any issues and I'll try to help.
sewellp@yahoo.com
Patrick Sewell, January 2008