Code:
<a href="pop.cfm" title="Open in New window" onclick="window.open
(this.href, 'popupwindow', 'width=300,height=200,top=50,
left=200,scrollbars=0,resizable=0,
menubar=0,taskbar=0'); return false;">
*
all code should be on one line
This should be it, although i typed it quickly from memory and I haven't tested it.
Put in the position (top, left) you want, or take it out.
I don't think you need px for measurements, but I'll soon be shouted down if I'm wrong.
Oh, and by the way, you should have posted this in the JavaScript Questions section of the forums