On Screen Size And Scrolling Problems

I have just reinstalled wnindows xp home on my dell dimension 5150 after a hard drive failure. The problem is that everything from icons, text,clock and taskbar  seem smaller on screen than before. its all in focus and fits on the screen fine but just that bit smaller than before the reinstallation. Also when i scroll its patchy and when i click and drag its not so smooth.This happens in both Explorer and other applications. I have set the screen resolution to 1280x1024 in the display options which is the recomended size for my monitor. Im lost on how to fix this problem please help.