I used to be a Mac Fanatic, but with the prevalence of Windows (including in my school) I've gone over to the dark side. I miss my Mac especially now that a Mac comes with iMovie and Garageband. These two apps made me consider buying a Mac mini, but then I realized I could probably throw money at my PC (probably less than I'd throw at a new Mac with extra RAM) and come close to both of those apps.
In fact I can get pretty close to iMove for free (since I have WinXP). Windows Movie Maker is free as is Photo Story 3. Movie Maker of course makes movies, it's not as slick as iMovie, but it is functional. Photo Story 3 is a great little program for making slide shows, it even includes panning and zooming ala Ken Burns.
That covers iMovie, but GarageBand is a bit tougher. Sony makes a program called Acid which comes pretty close, but is not free (Acid Music Studi0 $69.95). You can download Acid Xpress for free, but it is a bit limited and only comes with a limited number (8 or so) of loops. There are some free loops available on the net, but you have to really look to find them.
I suppose I should mention how GarageBand and Acid work. They stitch small bits of audio recordings, called loops, together to create original pieces of music. They are really quite cool and you don't have to be a musician to create some really good songs. GarageBand comes with 1000 different loops.
I did a search on Amazon to see f I could find Acid Music Studio for a lower price and was supprised to find Acid Music 3.0 for $4.00. So I ordered a copy. It won't do some stuff GarageBand or Acid Music Studio will do, but it is almost free. One thing it won't do is record, so you can't make your own loops with it, but you can use a free program called Audacity to do that. I'll post a review of Acid Music 3.0 once it gets here.
Sites I've found with Free Loops: