This explains how to add images to your posts. The key thing here is that the old smileys are referenced as images, not as smileys.
so [img]http://forums.auran.com/trainz/forum/images/smilies/confused.gif[/img] becomes
Consider the location of the image. http://forums.auran.com/trainz/forum/images/smilies/*.gif refers to the directory of the images, and the names of the images are the same as those of the new (smile.gif, biggrin.gif etc). Thus, if you put the name of the smiley onto the location of the old smileys, you get the old smileys appearing.
Well you can't legitimately use these ones directly. These emoticons/smilies/smiles were available from a website (I have long since forgotten where) offering their use for free as long as certain conditions were met. With Google and some time I'm sure you will be able to find a similar opportunity.