I've used both, for beginnners, go with windows movie maker, it's decent! it can cut, edit and get you something going, and yes, you can edit a good nice movie with it.
Now you want something more powerful, then move to premiere pro or vegas, and between movie maker and premiere, you can also try those basic editing software from Main Concept, Ulead, etc.
If you are new, learn the basic on NLE with movie maker first, then slowly grow up
Johnny Wu