I guess this can be a bit tricky, I've had people tell me about problems they have with it. I made a dance floor and put dancing on my bar, didn't think it was that big of a deal.
You would use the trigger box. Click on the new object button, search for trigger, click on it, then click create. I would first scale it to the size and rotation you want, then set it to the location you want. Go to the script tab and select the script Dance (or whatever kind of dancing you want - Dance Country, Dance Erotic). Under the state tab, click the little Advanced box. Then find and check Invisible and Trigger.
If you require additional help, please let me know and I will come help you.