Hi equinesites, and Welcome.
I don't think that's enough of the CSS code to be able to help without a guess or 2 ;) - e.g. is the menu horizontal or vertical.
It would really help to see all the code for everything inside the header including what margins etc you have on the floated
<img.. and how you're aligning the elements inside the menu itself, i.e.
display: inline or
Oh, and could you give the dimensions of the logo.jpg