I've been playing about 14 months, self taught so I could be WAY better if I had a teacher.

I got about 6 months till the talent show, and I wanna play some kind of metal song. Something that will make people who like rap say "that sounds really cool"

I dont wanna play something cliche like Eruption or Cliffs of Dover (like I could even play those)

I can't sing and play at the same time so I'd probably get a singer (if necessary for the song)
metal is so overplayed. get a drummer and play hotel yorba. easy to sing and play at the same time. matter of fact, its a good practice for learning how to sing and play.
No One Knows: Queens of the Stone Age
Not exactley a metal piece but its catchy and people will probabley like it, you can move it around too but probabley smart to get a drummer for that one, Dave Grohl has some great drumming on it.
Needs a double bass, suggestions?
I suggest a song by metallica, some of the songs are really easy. i would suggest mayb nothing else matters or unforgiven those are probably the easiest to learn and you dont need any effects
Some other dude is playing Beast and the Harlot, so I wnna beat that with some other metal song.

I'm thinking Two Weeks by All That Remains if I could nail the solo
from my experience, those who take themselves too seriously dont even win or get respect for that matter

just have fun n play a cool song, at my school the guitar gurus couldnt even be bothered competing lol. the one guy who did though played the metal by tenacious D and won
Since you have whole 6 months you could arrange a backing track for Rule the World by Kamelot and play along with it.

http://www.youtube.com/watch?v=qJeqUW-T5hE&feature=related Here it is. There is also a guitar pro tab with all the tracks tabbed here on UG.
"Fly with me forever high
And with these wings
We'll set the world on fire
Fly with me through scorching skies
You and I - The lie of lies"

-Symphony X
Dialectic chaos by megadeth, it has no singing, just crazy guitar solos. Or get a band and play some blues or something really different that no one else would think of, Beast and the harlot is such an over covered song at these events and such.