I found this in a few different places around the 'net - hopefully it's helpful:

Renew and Release IP Addresses

You can use the command-line tool IPCONFIG to get network information such as your IP address and to perform other tasks for troubleshooting network issues.

However, if you prefer a graphical user interface over command lines, you can download a GUI tool that will run on Windows XP and Windows 2000. The tool that?s installed is Wntipcfg.exe.

The tool identifies your IP address, subnet mask, and default gateway for each of your network interfaces, including the interface for your network adapter, your dial-up networking interface, and your PPTP interface. It allows you to click a button to Release, Renew, Release all, or Renew all when configuring an IP address.

To download and install the tool:

• Open the Windows 2000 Resource Kit tool download page Wntipcfg.exe: Windows NT IPConfig Utility
• Click the download link in the box at the top right corner of the page.
• In the File Download dialog box, select Save this program to disk.
• Select a location on your computer to save the file, and then click Save.
• In Windows Explorer, go to the location where you saved the downloaded file, double-click the file to start the installation process, and then follow the instructions.

To provide quick access from the Run line, install the program to C:\Documents and Setting\yourusername or the equivalent. Or, create a shortcut to the program on your start menu or desktop.

Yea if you want to disconnect from the network, in command prompt type in "ipconfig /release", and if you want to renew your IP address (sometimes there are clashes and errors with DHCP, rare) type in "ipconfig /renew". Typing "ipconfig" gives you your network IP details.