The following code simplified code example causes
the PHP.EXE (cgi-version) to hang IIS on my NT 2000 box:

$x = md5( date("aABdDFgGhHiIjlLmMnsStUwYyzZ" );

Note that calling md5() without using the date()
function works just fine.  So I don't know if this
is an error in date when it tries to generate such
a long date/time string, or whether it is the 
intermediate string value being passed to md5()
that is causing it to hoze up.  

To recover, one has to stop IIS and restart it.

I was using the 4.0.2 Win32 binary version from your
download section.