Road vs. Tri Bike

Okay, thank you for the replys to my previous bike envy post.  I realize that I am doing just fine on my Felt 75 and will continue to pile on the miles with that bike.

Another question -  Curious about a move to a tri bike.  I did two sprints in July and August and am doing to more in Sept.  I hope to train and move up to Olys or half irons next year.  

What are the differences between a tri-bike and regular road bike?   Should I consider stepping up to a tri-bike, given my goals.

And no, I don't have money burning a hole in my pocket - just curious.

Thanks all,
J