コード
function textAnable(obj, index) {
if (document.all) {
if (obj.checked) {
obj.form.elements["text" + index].style.backgroundColor = "#aaaaaa";
obj.form.elements["text" + index].style.color = "#666666";
} else {
obj.form.elements["text" + index].style.backgroundColor = "";
obj.form.elements["text" + index].style.color = "";
}
}
}
function gotFocus(obj, index) {
if (obj.form.elements["check" + index].checked) {
obj.blur();
}
}
<FORM>
<INPUT type="checkbox" onClick="textAnable(this, '1');" name="check1">
<INPUT type="text" name="text1" onFocus="gotFocus(this, '1');">
<INPUT type="checkbox" onClick="textAnable(this, '2');" name="check2">
<INPUT type="text" name="text2" onFocus="gotFocus(this, '2');">
<INPUT type="checkbox" onClick="textAnable(this, '3');" name="check3">
<INPUT type="text" name="text3" onFocus="gotFocus(this, '3');">
</FORM>