Like Kara says, just learn to FRED. As far as mission builders go it's the easiest I've seen.
There's a walkthrough in FRED that takes you step by step through building a fairly complex mission. It touches on all the areas that are really important (those that it ignores are generally very intuitive). Spend an hour or two doing that and you'll be ready to start trying your hand at FREDding.
I have a similar problem as you, incidentally: I have a near-constantly working imagination, and as such, I have several ideas that I think would make good stories for FS2. Currently I'm working on FREDding one of them. The problem is of course that my imagination is leaps and bounds ahead of me, and I can't possibly work fast enough to keep up!

FREDding your own missions is much more satisfying, believe me, and it's easier than it seems at first glance. Give it a shot.