The Locate Map Feature dialog

If you have downloaded the appropriate GNIS data, you can use this dialog to look up features that might be in the USGS's old GNIS data file.

You need to tell Xastir which GNIS file to search.

Enter the place name you wish to find and any supporting data that might help narrow down the search (state, county, USGS quadrangle) and the search feature should show you a list of matching names. Click on one and choose "Select" and your map should be centered on that place.