I've found the best ever free tutorials on how to make celtic knots (and other decorative knots!). I really never thought it could be so much fun!! But it is :-)
If you liked them a lot like I did, you can download them using
http://keep-tube.com
And here is the youtube channel of TyingItAllTogether
http://www.youtube.com/user/TyingItAllTogether
http://www.youtube.com/user/TyingItAllTogether