Your code will work, provided you have news and contact defined as constants (somehow I doubt you do). Even if you don't, it will still work, but is still incorrect coding, and will give an error message (which you should see) about an "undefined constant". As for examancer's case "default":, somehow, again, I think just default is really what you want.
At any rate, try some simple debugging:
echo $go;
switch($go) {
default:
echo "default";
break;
case "news":
echo "news";
break;
case "contact":
echo "contact";
break;
}
I suspect this is another case of assuming that register_globals is on when it's not. It shouldn't be on, anyway, so use
switch ($POST['go']