This idea makes it really easy to make great gifts using your own photos and you can even make customized calendars picking photos based upon the recipient.
I've used Inkscape in this tutorial, however you can adapt this to use what ever software that you feel most comfortable with as the techniques will be similar. Other free software choices would be GIMP or Paint.NET and while they each work a bit differently, the basic concepts of using layers to separate the various objects applies equally to all of them.
You'll also need some printable calendars for each month. A search online should find some results, but I've used some free calendar sheets from About's Rubber Stamping Guide, Kate Pullen. There's a selection of different styles available there.
This will be a perfect project for any new graphics software users as it offers quite a straight forward introduction to using layers, so if you've never tried something like this before, you've got no excuse not to give it a go.