Actually, thanks to http://flagrantdisregard.com/flickr/, The picture you want to use as its header doesn't have to be on Flickr, and you can save and print the resulting image to your heart's content.

Here's the one I made from a photo of my friend Kent:

http://flickr.com/photos/hauntedpalace/169684136/

If you upload the result you've created to Flickr, instead of just saving it, you can take advantage of Flickr's autoresizing. For example, here's the download page for the above photo:

http://flickr.com/photo_zoom.gne?id=169684136&size=o

Tip: the to-do list option is a little hidden; it's one of the frames: http://flagrantdisregard.com/flickr/frame.php. It's a choice in the pull-down list.

You can also create calendars: http://flagrantdisregard.com/flickr/calendar.php