Ask a friend to teach you the dance. Be sure to have plenty of space to learn the move, particularly since the first few steps are to "Move left, move right do yo dance on the floor." Since your coolness factor is directly impacted by your ability to do the dance at the right time, pick a friend who won't make fun of you or tell everyone that you never learned it. The best places to practice are in an empty gym, on an empty dance floor, in a backyard, or, of course, in your or your friend's living room.
Go to a club and watch people doing the Spiderman dance. If you can, sneak up to the DJ and ask him to play the song. Most DJs will be only too happy to oblige; more people dancing means more happy customers, and that means she's doing her job. As the song plays, walk nonchalantly around the dance floor and pay close attention to the moves. Another option is to ask a member of the opposite sex to teach you the dance. You could make the excuse that you were so busy with school you never had a chance to learn it. It's very likely that you'll get a positive response.
Use the miracle of the internet to find videos of people doing the Spiderman dance. Souljah Boy actually has a video that will teach watchers how to do the original Superman dance; no doubt, there is another that will teach watchers how to do the Spiderman dance. If you can't seem to find one, that's fine. Find as many videos as you can of people actually doing the dance, and practice in front of the screen. Be sure to move your chair so you won't hurt yourself, and close your door so you won't embarrass yourself. Before you know it, you too will be able to "Spiderman dat hoe".