changing radio button value depending upon menu selection

[wxdqz]

I have a form with the following structure:

(o) radioname=Sex (value=Know)
[menu] (values=empty, Girl, Boy)

(o) radioname=Sex (value=Guess)


I have it set up that if the user checks the Guess value, anything previously entered in the [menu] gets cleared out...works great.

However, I also want it to set it up that if the user enters a value in the [menu] AFTER checking the Guess value, that the radio checks the Know value.

This is what I have set up so far...

function processSex(obj){
if(obj.value=="Guess"){
document.formBGSetup.KnowSex.value = "";

^^this one is the one that works^^


function processSexMenu(obj){
if(obj.value=="Girl"){
document.formBGSetup.Sex.value = "Know";

^^this is NOT changing the checked value!!^^
^^how do I set this up to accept the values "Girl" and "Boy"^^
^^I have tested this by having it clear the value of a text field instead, and that works...?^^

Thanks!
~MVA