DScaler replaces the driver for the capture card. That's why it has to run at such a low level. It's not particularly unusual for a driver to need very low level access to hardware.

Basically it's their disclaimer, if it crashes then your PC will go along with it. If your video driver decides to go nuts then so would your PC as well.

DScaler output is nice though. I know somebody who has it piped through his projector and the improvement is definately noticable.

[edit]Whohoo... Pooh-bah...[/edit]