Is there a way to make an alarm system for your computer? say if someone were to move the mouse, click, or hit any keys on the keyboard, you could make certain programs or files run? what i really wanted is for a sound file to play and then have a gif image open up. Does anyone know how to do this?

If securing your PC while you're away from it is the goal, then you're approaching the problem from the wrong direction.

In display properties - screensaver you can set a password so that the PC can't be used by anyone else but the person who knows the password once the screensaver has kcked in

naw thats not it, i just want to see the look on my brothers face when he trys to sit down at my computer cause it looks like its on and stuff, and then when he touches the mouse a loud klaxon alarm playes and the screen goes red

ctrl alt del -> lock computer

In another words, gave a password for your user-profile.

Make a easy program, which you activate after leaving the computer. If another person "use" computer, then the monitor shows a nasty picture like Big sister is watching you, BSOF for few minutes....

or hold down the windows key and hit L

Or give another same mouse(unpluged) to the computer. Hide the plugged mouse somewhere and when he try to do something, yell on him, what he has done to it.