I have a dell xps m1530 which has been given a new

i have a dell xps m1530 which has been given a new hard drive- mine crashed with update on vista. anyway, when im typing in anything- yahoo email or even this box, my cursor jumps to a part of the text ive already written. i may be touching the mousepad with the pad of my hand but i think its done that even when im watching what im doing. there is no icon by my clock where i can control the touchpad sensitivity which ive read about doing to help. please help. thanks!