Frozen table header inside scrollable div

I’ve three divs. Header, central and footer. There is a table in central div (gridview) which is almost always longer than outer div. So I’ve made this div scrollable vertically. The question is: how can I make table header that it would be visible after div is scrolled down? I could have done this header with separate div or table and make it fixed but widths of columns in the table are not always the same – so I don’t know how to maintain widths of columns in header then. Any clue?

IFrame: This content cannot be displayed in a frame

I have two internal sites. I’m trying to show one’s content in the iframe of the other site. However I’m getting this message: “This content cannot be displayed in a frame.” I’ve read the reason I’m getting this message but, I would like to bypass it since the sites are internal and I’m not concerned with someone trying to hijack my users. I couldn’t find a way to bypass it after searching the internet, but feel like it should be possible because the rest of the message seems to hint at it.