Handful of screws
Sturdy tab-top curtain
1x4
Flat board (big enough to cover the 1/4)
Accent fabric (enough to cover the flat board)
Duct tape
First, you screw the curtain onto the 1x4 through the tab tops (we did one screw through each tab).
Then you screw that board securely to the wall above the window. Use as many screws as needed to get it really on there. We were able to screw it into studs.
Then you cover the thinner board with your chosen accent fabric (I duct taped it in the back).
Then screw that over the ugly 1x4.