Party Help!!

Ok, im 15 and everyone is having a house party!! And the thing is that I have never held a party before in my life! And if I do hold a party I have no idea of how to do it! And also I want to hold a huge party! Like approx. 100 people. And I want it to be the best party of the year! I need a theme! Something cool and creative! But not lame! I also dont want really to spend any or alot of money! I know the best music is everything, but do u have to book a DJ? I want this to be fun.. Cause there is going to be alot riding on this party for popularity reasons.
So if you have any ideas for themes for the party please reply to freelipstick_69@hotmail.com or reply on here!
Oh and i want to hold the party around the starting of June if that helps any!!

Thanx again!