James:

Windows Live Movie Maker is available for free download if you are running Win7 or Windows Vista Service Pack 2.

Movie Maker is pretty basic and quite straightforward, but does provide for limited transitions & animations; as well as adding music,title pages, editing, etc.


Also, iMovie is bundled for free with new iMacs. Otherwise it is available from the iTunes Store for $49.95. It runs on the iPad2. (Can be made to run on older iPad with a hack.)
iMovie looks a little more robust than Windows Movie Maker. Comes with themes and background music.

Adobe Premiere Elements9 is available for either PC or Mac ($54 after rebates from BH Photo) Much more functional, but with an undoubtedly steeper learning curve. Available for trial download at Adobe.

Jim