Contest/Voting Thread mod?

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I've never coded any php and I've been hoping that someone more experienced would come up with a voting thread type mod but I do have programming expeirence and it might take a while but I'll give it a try... I need some help though.

What I'd like it to do:
- Allow an admin/mod to designate a thread as votable
- Any member can 'vote' for the replies to that thread
- only one vote per member/per thread are allowed
- a member can vote for another reply in a thread, thereby changing their original vote

Additional but not necessary:
- usergroup permissions for 'voting'
- Automatic closing (expiration) of the thread and an auto post of a new thread for the winner w/original first post and winning reply included
- In case of a tie, an automatic PM to the admin/mod so a new thread can be posted for tie-breakers

I have a caption contest where I post a new pic every week and have people reply to it with captions. I go through and pic a winner myself but I'd prefer the members to pic the winners.

I think I've seen others needing the same thing for picture contests or similar activity.

Now... the important question.. how hard is this?

I'm a mainframe guy and have coded in many languages so the php isn't scary by any means, just different. I'd done years of DB2 so SQL isn't a problem.

For the type of mod I'm looking at, where should I start? What would be the best design? Any help would be appreciated. I'm not looking to sell this, I just want it and would like to contribute.

Thanks in Advance.