Centering main table with fixed position img

I have a fixed background with a table and what to position a logo dead center-top on the table (and stay there regardless what happens to the browser window)
I need to center in the table in the window as well.
here take a look.. and tell me what I need to do.

http://www.alpacahay.com/cinn
Do I need to change the table to a CSS Layout to get this to work?
Thanks...

#maintbl{
position: absolute;
width: 906px;
z-index: 1;
top: 0px;
}
#topimg {
width: 220px;
height: 130px;
z-index: 3000;
position: fixed;
margin-left: auto;

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