In the long run, it makes alot more sense to use something good that I've already made than to write another one and get about the same results.
Besides, I'm planning on writing a complete tile based map editor later in C#, so that it can have a suitable GUI. I was planning on doing it now, but I decided I wanted to focus all attention on the game.
However, should I try and write the map editor directly into the game? I think it would make the game seem more like a complete package. I'll worry about that later I guess.
I'm planning to have a little drop-down list in-game that allows the user to pick a custom level to play. This way I might encourage people to make levels and play other people's levels.
I may be getting a little ahead of myself though, I haven't even made the menu screen[grin]