Do you have a Widescreen monitor? DR plays in 4:3 Screen Ratio and I don't believe it can be changed to widescreen(16:9 I Think)
I also have the bars on both sides aswell but I choose to play that way. My monitor can stretch it out for full but I hate stretching what I see.
Now if you have a standard 4:3 monitor and display windows in resolutions like 800x600, 1024x768,and 1280x1024 while still having the black bars on both sides, then you really got a problem there o.o.
My 16:9 ratio view windows in 1920x1080.
And if you got the widescreen, you can't really do anything bout the black bars except stretch the screen to fit... Unless there's something I don't know about o.o
[Edit]
Maybe this'll help explain:
