Why does the background image disappear when float property is used

I have created a container div tag to hold 5 columns which I want to be side by side to each other. The div tag holds a background image of 600px wide and 1px high which is set to repeat y so as to create a nice background behind the columns.

The problem is that when I set all the columns to float the background image disappears behind the columns.

Why is this happening and how can I get the background image to display behind the columns?

Thanks

You need to clear your floats! See www.quirksmode.org/css/clearing.html

May I see this HTML script page of yours.
Regards,