How do I fix the blurriness when I change my screen resolutions?

I recently got the MS Blaster worm and had to get my computer reformatted (Windows XP). When I got my computer back and connected it to my screen, it was off centered with a big black vertical bar on the left side. So I went to my properties and lowered my settings to screen resolutions 1280 by 800. The screen is now centered, but all of my features are blurry. The icons are slightly stretched vertically and the text is barely legible. This computer and monitor make is a HP Pavilion f1703. How do I make the blurriness go away and fix everything so that it is normal?