Please note, I have FW but not MPG Edn, but assume the Map Editor's the same.
The map editor only places the starting point for the tribes once you begin the game on a pre-made map - as such, it doesn't actually even place cities, you need to build them once the game starts.
When developing a scenario, it is advisable to change the settler movement rate (in rules.txt) from '1' to '0' - that way they don't go running around should you accidently end your turn. Change the movement rate for the settler back once you have your game set up though!
Avoid ending the turn - the AI will take run your tribes for a turn, which can have problematic results, and you may need to resort to the autosaved game to start again.
So, start with the white tribe on a pre-made map. Reveal the map in cheat mode, and start plonking down settlers where you want cities to be. Use the wait ('w') command (if required) once you've placed your settlers to cycle through them until you get to the one where you want your capital to be. Build your white tribe cities, but do not end the turn. Using cheat, swap over (Set Human Player) to the green tribe and do the same, then dark blue,...
Once you've finished with the purple tribe, go back to the white tribe where you can start changing the city sizes and adding units, city and terrain improvements, and revealing the map by tribe (as you consider appropriate). Be careful with Wonders - once placed you're stuck with them! Save often.
Moving a city is a pain, and it's best if this is never an issue you need to deal with. Two possible approaches include - creating an events file and an event that will trigger a 'changeterrain' action on the city's tile/square (see macro.txt in your Civ2 folder for info' on events). Alternately you can 'almost' build a settler with the size one city and play the game for a turn, where ideally you will be given the option of eliminating the city.
Should you have settlers placed in the wrong position for whatever reason, use 'Destroy All Units at Cursor' - although always leave at least one settler or one city, or else you'll destroy the tribe.
[This message has been edited by Cam (edited March 08, 2000).]