Blocks Collapsing

Could you take a quick gander at this site please and help me understand why the white block has moved up into the header div please.

Only in IE/win :-)
Actually: the white block doesn’t really move up, but the header collapses because there’s only floats in it, so the white background on wrapper doesn’t get properly covered by the background on header.

Give IE/win a well-placed ‘hasLayout’ trigger…
#header {
height: 1%;
}

…and it will behave and paint backgrounds as intended.