You didn't mention the OS, so there's two possibilities.
For DOS versions of Windows (Win9x/Me) you can type in "winipcfg" or something close to that (been a few years for me), and it will have it somewhere in the box that pops up.
On NT based systems (NT/2000/XP) type in "cmd" then "ipconfig" in the DOS Prompt that shows up. Why MS didn't simply supply winipcfg in these OS's is one of life's many little mysteries which probably has no satisfactory answer.
What do i type in Run to find my IP address