Hi Jon,
Solved!!! Turns out it wasn’t Quicktime nor the drivers, but a conficting app bundled with the graphics card. It is an ASUS Matrix GTX285, an “enhanced” version of the GTX285 that comes with bundled software for overclocking, online surveillance an video capture (of games, I guess).
After removing such extras it works like a charm. I’ll be using it without the “enhanced” features, but the actual reason why I chose the Matrix was the deal I found (200$ including shipping).
Thanks anyway!