Leave DEP on
The app doesn't matter, and has nothing to do with this.
Sorry. No. You are flat out mistaken. I will even proceed to tell you why, even though it is blindingly obvious:
DEP enables a feature which protects memory pages from writing. The point is to protect executable code from being written to by malicious code (or due to bugs in the software). A buffer overflow attack will be more difficult to conduct (near impossible), since it is (at most) limited to corrupting the stack, and effectively tightens most holes.
Windows NT had this feature already back in 1993 on most CPUs that it supported, except for Intel's family of CPUs.
When AMD introduced the Opteron line of CPUs, they simply added DEP as a feature and Windows apps could once again benefit from this protection. Since PAE extended the memory page header, they had enough room there to add the necessary flags. (thus DEP can only be turned on if PAE is enabled, or in 64-bit mode)
All the relevant API have always been there! There are absolutely no news here for the app developers; Just sloppy reading of the docs!
It is down right sloppy coding on Cyberlink's part that caused you grief. Cyberlink, and they alone, are to blame. Let me put it in a way you can understand: Cyberlink are a bunch of idiots.
On my system, I had to pull three SCSI optical drives, because PowerDVD would otherwise refuse to play any DVDs at all, even from my SATA drives. That is not Windows' fault. In fact, an older version of PowerDVD worked just fine. The new one fails. All other players just work. PowerDVD fail, fail, fail.
Cyberlink's support suggested that I should check what HDMI cable I'm using... As if that has any bearing at all on my SCSI drives...
They are crooks as well as idiots.
Vista may have its set of issues, but in this case I think you should realise that the OS works as designed, the app in question (PowerDVD) DOES NOT!
Do you still have any questions?