For basic video editing features like music, transitions between clips, subtitles and credits...as everyone else has already said, Movie Maker. A very nifty little tool.
If you start craving more power and editing options, you might want to check out
VirtualDub or
VirtualDubMod (I personally prefer the latter). Most of the power of the program lies in the menus at the top, don't be afraid to mess around and click things at random to see what it all does.
Some people complain that it takes a bit of getting used to, which it does...but there's a lot of power there. There's a large amount of tutorials online if you have a specific task in mind, like cropping/resizing a video, adding audio or subtitles, what all the filters do, etc.
Last but not least...even though it's big, clunky, slow, and the interface is ridiculously annoying, at least to me...there's
SUPER (C). Makes trans-coding audio and videos from one format to another a breeze. Just set your options like format you want to save as, (avi, mpg, etc,) resolution, audio quality...then click Encode and you're done. (I sometimes use this to get WMV files from Movie Maker to AVI so I can continue editing the video in something like VirtualDub.)
If you ever need to figure out how to do something with video or if you're looking for a video tool or utility,
videohelp.com is a great resource to look into.
Hope that helps somewhat. None of these are as good as some of the better commercial programs that are out there, but they can get the job done.
