Thanks to respond.
But I didn"t install the ATI Control center, it's heavy, and mostly useless. I'll search an other way to force the scaling.

I'm quite sure any solution is going to involve, possibly severe, stretching. 2D games are very unhappy to have their aspect ratio's altered.

This does not work on all computers as some of the hardware manufacturer has locked the drivers settings. What I would do is uninstall your drivers through device manager and make sure the "delete driver software" box is ticked. Reboot your computer and then let Windows Update install the driver package without extended features. A regular user like you and I might not care about the extra settings just to play something normal like this.

Try checking/unchecking "aspect ratio fixation" in the game config program.

Some monitors have the option to stretch the image to fill the screen. On my monitor this option only shows up when you are using a resolution lower than the native one, I would try launching the game and then search through your monitor's menu.

Well I given up and installed the controll center.
If anyone find one day an other program to scale the image, please PM me.