There are two elements to your question:
- What tools do you need
- Where do you get the skills you need?
The tools are free, and the links above are fine, though I would probably start here In any case, you do need some form of Visual Studio 2010 but we have a free version especially designed for the phone. All you need besides that are the (free) Windows Phone 7 Developer Tools, though I strongly recommend picking up the documentation and guides.
As for learning WP7 programming, you have many choices. Many of the best are discussed in the Windows Phone Team Blog.
In addition, we have numerous videos on Silverlight.net and I have an couple of on going mini-tutorial series (one targeted at Silverlight programmers and one at iPhone Programmers) on my blog.
There are also lessons, and much more coming out every week.
Best of luck with it and let us know how it goes
-Jesse Liberty
Senior Community Program Manager - Silverlight and Windows Phone 7
Microsoft