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Although, having said that, I think IE can be configured to block ALL popups - although it is not the default setting. The Googlebar may be similar?
Bare in mind that the code example you give will not work if JS is disabled. Ideally you should set the href to point directly to the file and activate the 'popup' in the onclick event, that way the file can still be accessed if so desired:
<a href="mypopupfile.html" onclick="OpenPopUp();return false;">Click to open popup</a>
If JS is enabled, they see the popup, otherwise the file opens in the browser.