Is alert / msgbox a modal or modeless???

Hi All,

We are facing a typical problem in one of our application.
We are popping up a message using msgbox method on an HTML
page (IE 6.0). The user should not be able to do anything
on the HTML page until and unless he clicks the OK button
in the msgbox displayed. i.e, the msgbox displayed becomes
a modal window for the HTML page opened. But the same HTML
page when opened on tester's machine (IE 5.5), the msgbox
is displayed as Modeless and the user is able to access
the HTML page behind.

As far as I know the msgbox is Modal (by default) and
waits for the user's response before allowing him to do
other operations on the page. Please correct me if I am
wrong.

Can anybody please let me know if there is any setting on
IE that makes the msgbox Modeless OR as to why this is
happening? Is this because of difference in IE versions?

Awaiting for some quick responses...

Thanks in adv.

Regards
Naveen