php5 on IIS6 (CGI Error)

hi! i'm running a test-server with windows 2003 and IIS6 i managed to get PHP 4.3.2 running without any problems. but i wanted to try php5 so i downloaded the zipped version renamed c:\php to c:\php4 and extracted everything to c:\php (so that the old php.exe is "replaced" by the new one) for the old version everything worked fine - but now i get the following error: CGI Error The specified CGI application misbehaved by not returning a complete set of HTTP headers. did somebody experience similar problems? is this only because its a beta or is this a configuration-problem? thx in advance, matthias