anyone have any tips on cutting some .5 inch plexiglass and get a good edge? im going to be making a computer case out of it.

Here is good link.
http://www.sdplastics.com/polycast.html
Here is another one not so much on cutting but more on gluing and set up.
http://www.advancedaquarist.com/2007/7/diy

Jigsaw with a fine metal blade, then sand it down with some 60 to even out any bumps. Or better yet, clamp a straight edge to the work the distance from the blade to the edge of the blade guard away from the cut line, then go at it. If you keep enough sideways pressure so the guard stays square with the straight edge, you should get a damn nice cut.

As with all projects, do some test runs on scrap before you go at it on the good piece. My jigsaw's blade is angled for some reason and this method wouldn't work, so just make sure by doing a test cut first.

I have always used a scroll saw with a fine metal blade or a bandsaw with a metal blade. Make a fence out of a straight piece of wood and dont try too feed the polycarbonate in too fast or it will start to melt and bind up your saw.

After you have made your cut use fine grit sandpaper to smooth out the edge and use a buffing wheel if you want the edge to be crystal clear and not opaque.