KeyPress Capitalize Function Broken In IE9

A common javascript function that capitalizes input as user types (onkeypress) no longer works as of IE9Need a function that also works in IE 9 that doesn't not change method call or interface (as it's used in 150 places throughout application).

CALL:
[CODE]
el.onkeypress = function(el) {
return c_capitalizeInput(el);
}
[CODE]
FUNCTION:
[CODE]
// Intercepts keyboard input and capitalizes keystrokes.
// Call with onkeypress="return capitalizeInput(event);"
// Compatible with both IE and Netscape/Mozilla
function c_capitalizeInput(evt) {
evt = (evt) ? evt : ((window.event) ? window.event : "");
if (window.event) {
// IE
if ((evt.keyCode >= 97) && (evt.keyCode <= 122)) {
evt.keyCode = evt.keyCode - 32;
} return true;
} else if (evt.which) {
// Netscape and Mozilla
key = evt.which;
if ((key >= 97) && (key <= 122)) {
key = key - 32;
evt.target.value = evt.target.value + String.fromCharCode(key);
return false;
} return true;
} else {
return true;
// Can't do anything for other browsers
}
}
[CODE]
How to make this work in IE9?