Without accessing to certain websites to check for an IP address of your internet connection, you can use the following command.
For Windows XP:
1. Click Start button -> Run
2. type cmd -> click OK
3. The MS-DOS Prompt screen will pop up, and then type ipconfig or ipconfig /all to see other subnet mask, defaut gateway, dhcp server, dns servers, etc…-> press Enter
For Windows Vista:
1. Click Start -> type cmd -> click OK
2. type ipconfig or ipconfig /all, then press Enter