This is not really a tweak, but give you a little overview how to use the Windows XP SP2 Firewall to open ports or adding allowed programs.

Start Firewall Control Panel:

1. Click on Start -> Run
2. Enter in firewall.cpl
3. Click on the Exceptions tab

Adding a Port for Internet Access:

1. Click on the Add Port button
2. Name it whatever you want
3. Enter in the ports you want to open

Adding a Program for Internet Access:

1. Click on Add Program button
2. A list of all installed programs will be displayed
3. Highlight the one you want to include for Internet access
4. Click on the OK button