Kiera, I'm assuming you don't have a mac, only because they come with imovie which will allow you to do all you're wanting to do with that format. Also, you mentioned windows movie maker...
So, can I assume you have a PC? The easiest/cheapest way is to convert them -
http://www.videohelp.com/tools/Rad_Video_Tools That should work. There are so many converting programs, just godda find the free ones. I'm sure the one Norman linked you too will work too.
If you're wanting different software, adobe products are great. I use premiere pro and it's all I use. Can do just about anything. But it's expensive and it's a little complicating at first. If you're just need some titles and simpler stuff, I'd just convert and use WMM.