Shimano Duel SIS 7 speed rapid rise shifters
 

Has anybody ever hear of these shifters? I have these on my Trek and they are crap. I looked on the net for some info about these and I have found nothing. Is there a way to adjust these shifters, or do I have to replace them? Is it possible to make a bike shift better if the shifters are replaced? I have a Trek 7200 Multitrack. The bike is a 7 speed with 3 chainrings up front.

Yes, they can be adjusted. More expensive shifters would probably improve the shifting, but your current shifters should perform OK once you get them adjusted properly.