I am planning on creating a new map I had in a dream of mine (Yup, you heard right )
I actually had a dream about a tribes 2-esque game and I specifically remembered how the terrain looked. Thinking about it now I believe it would make for a very interresting map!
Sorry bloodness, but there isn't a "new mission.mis". I believe the new mission feature of the editor was never completed. The best way to start a new map is to make a copy of an existing map that is close to what you want and modify it from there. There was a server-side starter pack with blank missions for each terrain, but I can't find links to it anymore.
I'm kinda surprised noone had answered your question, but you did post it in the wrong forum and started hijacking other threads. (Tribes Vengeance is a completely different game from Tribes 2 and has almost nothing in common)
Ultrasonic:
I've done that before, but it didn't end up too well. We're able to answer most questions about T2 mapping, so don't hesitate to ask (don't forget about the search function too!)