Johnny,
We go there regularly around the first week of March. For most of our trips over the past dozen years the weather has been pretty good - mid-70s to low 80s, lot's of sunshine - but we've also had cool weeks and rainy/windy weeks at that time of year. It seems to me that the weather starts to stablize more in the second week of March and later (locals have told me that that's when the first real beach weather starts) but, for the most part, we've been happy with our early March weather. So I guess what I should be telling you is that it can be a bit of a crap shoot but, for us, even when it's coolish, it's better than the winter weather that we leave behind in the northeast.
Crowds at the parks are large but manageable. Lot's of public school vacations at that time of the year but the crowds aren't as bad as they are for the Presidents' Day holiday week in February.
I'm expecting great weather and moderate theme park crowds for the first week of March 2009 - as we'll be in Orlando again for that week!
Dick Taylor