Problems with my layout

[SRD]

Hi, I've been trying to re-invent the wheel and design my own layout with two full width divs above two part width columns above two full width divs.
http://myweb.tiscali.co.uk/simonrive...inkscheme.html
with the css at
http://myweb.tiscali.co.uk/simonrive...linkscheme.css
The first of the two lower full width divs spreads beyond the right hand side of the right hand column and I can't work out why, if any one can suggest a way to bring it back under control I would appreciate it.

[junjun]

Just remove the width: 100% on #sponsor and it will adjust to available width.

[SRD]

Thanks a lot, so why does that happen?


edit:
More to the point, why is available width less than 100%?

[junjun]

You added padding and border, which in the box model goes outside the width of the box. But really it's not a problem because you added width, which in your scenario here is redundant. A block element will always take up available horizontal space.

[SRD]

Again thanks, every day a little more is learnt.