I experienced the exact same problem with this product. It's unfortunate, because it really is an awesome monitor, and it does look better over DVI.
I have found a solution , although it involves money . I bought a new graphics card. Previously, I was using a Raedeon with ATI technology and, fearing that a repeat of the problem would occur if I bought another ATI-based card, I went with Nvidia this time. The new card is a GeForce 6200, and it solved the DVI problem.
The unfortunate thing is that EZTune is incompatible with the new card; launching EZTune with the new card causes my Windows XP Professional-based PC to completely freeze. The only way to unfreeze it is to reboot (in Safe Mode if EZTune is set to start automatically). This happens whether EZTune is launched manually or automatically. The monitor's optimal settings (such as resolution) can be set through the graphics card's tools, but without EZTune, the monitor cannot be rotated to display in Portrait Mode.
With luck, there will be an update to EZTune in the not-too-distant future (the current verison is only version 1.0, which means buggy-as-**** in technical terms). In the meantime, I prefer the superior picture quality to the ability to use Portrait Mode.
