First Triathlon ever...Questions

Adam, Sure you can ride a MTB in a triathlon-lots of people will on their first couple.  After that you need to ask yourself  "What am I trying to accomplish?"  Podium finish, PRs or just enjoy the thrill of the competition and training.  If you want to get faster, you'll eventually have to get a road/tri bike.  BUT, there are some things to do to help the mtb scoot along better.  Get tires as narrow and as smooth as you can-then pump those suckers up to the max.  If you have bar end extensions that slide OVER the bars-you can move them inboard past the brake/shifters to narrow your frontal area a bit and make you more aero.  OR-you could not change a thing, don't lose a minutes sleep over it at all and have a BLAST on your first tri.  Welcome to BT-Good Luck!

Thank you so much for your post!  Where is a good place to buy tires?  I'm assuming I should also get rims with it so i don't have to keep changing my tires out.

You can buy tires at any LBS or look online at Performance or NashBar etc.  HOWEVER, once you start buying new rims too, you change the cost equation from 30.00 (tires only) to 200.00 (tires and wheels).  For 200.00 you can buy a used roadbike on Craigslist.   Just a thought.....

Good thought...do you know of anyone with a cheao bike.