ATI's DDO is simply an alternate third interface to the Windows setting (in dxdiag and also properties cpl). So if it didn't work then there's some other problem with a combination of the DX/OS/graphics install and trying to "work around" it with a third-party utility is a bad idea -indeed I've seen them be the cause of the problem in the first place. ATI also added OGL functionality to their interface years ago.
Anyhoo, the relevance is severely on the wane since the popularity of LCD, increase in properly developed games (oh look the user can actually choose the resolution and frequency ooh aah, welcome to the new millennium), and finally if absotootly necessary for dodgy old games then the functionality has been included in driver control panels as said, in addition to comprehensive tweakers such as ATI Tray Tools.