A nice utility in Windows 2000 / NT 4 is ipconfig. Invoke it as follows:
1)click on Start, then Run, and type in "cmd"
2)on the prompt, type ipconfig
This will give you basic info on your IP address, subnet mask, and gateway. To get more information such as DHCP and DNS Servers, type "ipconfig -all".
In Windows 9x you can use a utility called winipcfg instead.