Windows Movie Maker is actually a pretty powerful software for being a stock install on the PCs. I used that when I first started out, and I made some pretty nice little videos with it. Video editing is the kind of thing that the old expression "practice makes perfect" comes into play about. I spent the first year or so of my editing career (before Firehead Studios came about in 2005) just messing around with the software and making compilation videos. I was surprised too when I found that I had editing software on my computer!
A lot of it is just trial and error. Limewire is a great tool for getting music for videos. As far as matching pictures to the music, in the program, you can either go by a song that you know and put the switches to the beat, or watch the sound progression of the song in the audio track.
It will just take some getting used to. Windows Movie Maker was great for my first little bit with Firehead, but after awhile, I outgrew it. Now, I am using Sony Vegas 6.0 to do all of my editing. This is a great, powerful software that I am still learning how to use even after a few years. I would recommend the Vegas software to anyone, and I believe that they are up to Vegas 7.0 or higher now. My 6.0 software is awesome for what I need, and I would look at either that or Sony Premiere Pro. Premiere is VERY expensive, but very worth it if you are going to be doing a lot of video editing. I have stuck by Sony products since I started doing studio work, and I will stick by them for the extent of my career.
If you do upgrade to a more advanced software, be prepared for a steep learning curve until you get the software figured out. Once you do figure it out though, it is like making the transition from a point-and-shoot camera to a DSLR one; you don't know how you got by before without it.
PM me if you have any questions about Vegas or want any more info.