This is the best map of Prague we could find:

http://www.mapy.cz/

If you click on Praha 1 four times, you will zoom in close enough to see the street names. Unless you speak Czech, though, don't expect to get a handle in your whereabouts too quickly. Your hotel will undoubtedly have a map that's more tourist-friendly. It's actually fairly easy to find your way around the city, once you get there.

Regards, Don and Linda