Online Contests

Where can I find legal information on holding online contests in the US ( I reside in West Virginia )? I was looking at other companies that held them such as Dell & Tiger Direct and noticed that they required the winner(s) to complete an Affidavit of Eligibility, a Liability Release, and where lawful, a Publicity Release. What are these documents and how should I go about obtaining them and knowing when a Liability Release is required?

Also, I notice some competitions say you must be 13 years of age or older or have parental consent, others say 18 years of age. Which is correct and how can you verify the winners age(s)?

I'd also like to allow participants from other countries into my contest, are there other requirements I need to know about?

Thanks