You could try this assuming that your header has a fixed height.
Code:
#navColumnOneWrapper{
margin-top:-200px;
}
That assumes that the header has a height of 200px. You'd then want to put a left margin on the div #headerWrapper so that it didn't overlap the left column.
I believe that there are a few issues with negative top margins in Internet Explorer (6 and 7 off the top off my head) which cause a flickering in some circumstances. I also believe that this isn't one of those circumatances but I may be wrong and you'd need to check it thoroughly.