Simple 3 col layout with CSS

hi there … im trying to work out a 3 column header for a site …

where i have a flash menu in the header set at a width of 960px. And either side of the flash menu, I want the two other columns to repeat the bg.png so that it seemlessly fills to the side of the browser. Thus the flash is centralised.

so basically it looks like::

<header>width:100% height:26px.
<cleft>has a background, at width ? auto?
<flash>width: 960px height:26px
<cright>has a background at width ? auto?
</header>

Can anyone give me a hand with the css?! I have had a go with floats and clearing etc … I just cant do it when the flash is involved!

thanks!!!