Function Validate Assistance

My validate() function is not working quite right since it should validate for at least on checkbox checked and even if opne is checked it will simply display the error message instead of validating. What might be wrong here?

Here's the function (note, all the checkboxes have the id='chk')

function validate(){
var countChecks = 0;
if (document.forms.getElementById == "chk")
{
for (var j in document.forms.getElementById)
if (j.checked)
countChecks++;
}
if (!countChecks)
{
alert('Select some checkboxes!')
return false;
}}