Preventing Onkeypress Events In Netscape 7 For Mac Fail

I have a web page where I want to intercept keypress events in an INPUT-tag
and check if it is the Enter key, which calls another function that executes
a search. My code runs on Netscape 7 for Windows, IE 6 for Windows and IE5.1
for Mac, but not on Netscape 7 for Mac. When I press the Enter key, the
event gets caught but it does not get prevented and the search is never
executed.

The code looks like this:

function KeyDownHandler(e)
{
// if not Netscape, get IE event
if ( !e )
e = window.event;
if ( !e )
return true;

// Get valid ascii character code
var key = typeof e.keyCode != 'undefined' ? e.keyCode : e.charCode;
// process only the Enter key
if (key == 13)
{
// cancel the default submit
if (e.preventDefault)
e.preventDefault();
else
window.event.returnValue=false;

// submit the form by programmatically searching
search();
return false;
}
else
{
return true;
}
}