How do you alt tab in HL 2?!
 

Whenever I alt tab it takes the last screen I was tabbing from, and flickers it rapidly like a strobe light while showing what I alt tabbed to. Is there a way to fix this from happening?

Uh, Alt + Tab works for me in Half-Life 2. Check VALVe's forums to see if other people have had the problem or fixes.

Have another window open before you play.

hit the windows key on you keyboard and use the quick lauch next to the start button to show desktop always worked for me in just about anygame that will not alt tab out of it. (remembers doing that in doom 3 when pinkey shows up for the frist time and missed it)

Windows Key+D should work also. It minimizes all windows and shows the desktop.