Warnings w/ !$var!?

I just installed PHP4 on a Windows 2000 box (tried it both as CGI and ISAPI) and am getting a very annoying behavior from it, that I do not see on my installation in Linux. When I check a variable (say, in a if() statement) via !$var, I get a Warning message printed saying that it is not initialized (if that is the case)... well, that's part of the reason why I bloody doing the test! In my Linux installs this doesn't happen and in every program language I know this is a valid check without warning... why do I get on in Windows PHP!? Is there a config variable I can set somewhere that will prevent these Warnings from printing? I am aware of the isset($var) function, but this does work for my purposes. Nick