Funny that, I will be doing my first Promo (for a Wedding Car business) in the next month or so.
Oddly enough what is important to me, isn't the choice of software (I will use Premiere Elements or ULead MediaStudio), but what message and what styles the client wants to cnvey to his potential customers.
I will spend quite a bit of time with the client, and I will look at his existing promotion & marketing material. I will alos ask him about his competitors and find out what he thinks makes his company that little bit better (Service, Quality of Cars, Professionalism etc).
From all of this I will preapare a number of prototype scripts then discuss. I will then finalise the script and prepare a shooting plan. Filem, edit and present to client. make appropriate adjustments following that and then go to final burn.
So the software is entirely secondary in this instance. Although without prejusging the client's wishes, I would expect to use software that is capable (and indeed good at) fairly standard editing functions (Multiple Layers, perhaps a little colour pass here and there, and from which I can prepare the final DVD. Now I would be the first to admit that Movie Maker has moved on from its first incarnation, but it is still a beginner's tool and lacks any DVD Menu Creation functionality. If you don't want to spend a lot of money on your project, then you could do much worse (IMHO) than Adobe Premiere Elements.
Good luck with your venture!