>Lets assume the fact that I have a main container with several IFrames at the same level. Thus, I could have one IFrame on the left and next to it, another IFrame with about the same height.
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>When I do a specific operation, I need to obtain the exact pixel in width from the browser itself. I can determine the width offset of a specific Div on that page. But, in order to position something exactly where I want, I need to also obtain the width of the IFrame sitting on the left.
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>So, basically, the IFrame on the right knows about its parent. In this case, it is the main container. But, it doesn't know anything about the IFrame on the left. It could, but I would have to hardcode it such as window.parent.TheFrameOnTheLeft.scrollWidth. But, I need a generic way of knowing it. Is there somekind of formula I could use to obtain all the frame sitting on the left side of the frame I am working with, no matter how much frames there would be?
Why not give them specific IDs? Then get one by one by Id (getElementById, or $("#id") in jQuery), and you got your object reference to each.

If you don't know in advance how many of them you may have, then it's a bit tougher. I'd go for all iFrames (get...ByTag), then comb the collection for the ones that share the level (i.e. same parent) as your iFrame.