Those are both horrible examples to use, sorry to say. The first is a video we have all seen a million times, and is obviously someone who has been doing this a VERY long time and has a very well set up car for such an event. I highly doubt anyone that will be attending your event will be doing anything near what was shown in the first video.

And the second video, as dope as it is, I wouldn't really call it Gymkhana. Although Ken Block shows some VERY technical moves with his Subaru, and the video does show a few very common aspects of Gymkhana, the speeds, and the drifting done in the video are incredibly overexaggerated, and once again I highly doubt anyone that will be attending your event will be doing anything near what was shown in the second video either.

Perhaps you should check this video out, and see some amatuers, at a Gymkhana event in a small parking lot, where (from what I understand) is where these events really started.

http://www.youtube.com/watch?v=dgXlgxpYVfU

There is a lot of sliding going on, but nothing I would really consider to be "drifting".