Screen Display enlarges while moving cursor

I recently purchased a Dell Studio 1737. The OS is Windows Vista. I have a problem while navigating on any page, the screen will either enlarge or minimize in size on its own. There is a "100%" symbol on the bottom right of my screen, but while moving the mouse / cursor, the screen will either enlarge to 125%, 150%, or larger, or downsize to 75 or 50%. I then have to point the cursor on the bottom right and click once and it will return to 100%. This is very annoying, I don't know if this is a Dell problem or a Windows Vista problem. My previous notebook was an Inspiron 9000 series and I never experienced this problem before. I would appreciate anyones input or help. Thank you all in advance.