You use photoshop for science? Do tell
Maptool is a great program, and there are now a lot of maps out there to use, not least of which are the WotC Dungeon maps that are put up on the web without the labels on. Start using those, and then you'll naturally graduate to making your own. Post a map in the WIP section and you should get some good feedback. If you need focused critique, then you can always pm people and you'll get a response as the site's got pretty large so I know that I don't get a chance to see everything that's up every day.
Welcome to the guild!