Código HTML:
<html>
<head>
<script>
function checkRadio(valor){
var radios=document.getElementsByTagName("input");
for (i=0;i<radios.length;i++){
if(radios[i].type=="radio"){
if (radios[i].value==valor){
radios[i].checked=true;
}else{
radios[i].checked=false;
}
}
}
}
</script>
</head>
<body>
<form>
<input type="text" name="texto1" onFocus="checkRadio('valor1')">
<input type="radio" name="opcion" value="valor1"><br>
<input type="text" name="texto2" onFocus="checkRadio('valor2')">
<input type="radio" name="opcion" value="valor2"><br>
<input type="text" name="texto3" onFocus="checkRadio('valor3')">
<input type="radio" name="opcion" value="valor3">
</form>
</body>
</html>