Simplest way to add stills to MP3 audio soundtrack
I think iPhoto will export a slide show with audio as a movie. If you want more control then an auto advance slide show then use iMovie.
In iMovie create a new project, add your audio track and then add still images along the time line.
Both Mac and Windows ship with video editing software built in. I'm on a PC right now so I can't comment on Apple's version, but Movie Maker on your Windows machine is pretty easy to use and is more than capable to do what you're asking.
For simple slideshows you can also use PowerPoint.