Do Events Run in Threads?

I'm using IE 6.0 for Windows.

I have a table with several rows where each row has a column that contains
two checkbox controls ("approve" & "reject"). A form (separate from the
table) is submitted each time one of the checkboxes is clicked and the
response is targeted to an <iframe> on the same page. I would like to be
able to prevent the user from clicking another checkbox until after the
response comes back from the form submitted.

I've tried handling this by setting a global variable to true whenever the
form gets submitted, but that doesn't seem to work all of time. If I keep
clicking very quickly I can sneak multiple submissions through. I'm trying
to figure this out and all I can come up with is that perhaps IE (and
perhaps other browsers) run events such as onclick in their own threads?

Is that true? Anyone have a good idea of how to code something that will
prevent another form submission until after the response comes back from the
form?