During our testing, we were faced with what appeared to be pretty big teething issues with 1080p playback on both the 8400 GS and 2400 PRO cards.

Let's start with the 2400 PRO. This is one hell of an issue, as all of the 1920x1080 content was played back at a maximum resolution of somewhere around 1440 pixels wide. This means that if your desktop resolution is set to more than 1440 pixels wide, the 2400 PRO would display HD content in a box with a black border around it. Yuck!

We found a registry tweak hack on the 'net that would allow the 2400 to output video at the full 1920x1080 resolution (AVS Forum - Home Theater Computer), but it only seemed to work for us in Windows XP, and only if the 'pulldown detection' setting was disabled in the Catalyst drivers.

When we asked ATI about the problem, they let us know that they had intentionally limited the output size on slower cards like the 2400 PRO, because they were worried that HD video would choke on them. However, they also promised us that the upcoming 7.11 Catalyst drivers would remove this limitation, and allow even the lowly 2400 PRO to display 1920x1080 video. So we'll be checking up on their promise in a future review.

While the 8400 GS thankfully had no screen-size limitations or borders, we did experience a lot of 'flashing' during playback. That is to say, it seemed as though some frames were randomly flashing bright white. This was very distracting, to say the least, and I don't think we'd sit through a movie on the 8400 GS if we didn't have to. At the time of writing this, Nvidia hasn't gotten back to us about this problem, and we can only assume it's a driver glitch that they'll address in the future.

So there you have it. Although we benchmarked both the 8400 GS and 2400 PRO in this review, take all of the results with a grain of salt as neither of these cards are viable 1920x1080 performers quite yet. At this time, the 2400 PRO is viable either on a 1440x900 or lower resolution, or in Windows XP with the registry tweak mentioned above and 'pulldown detection' disabled. The 8400 GS was not viable for viewing HD DVD content at all on our test system, and though we assume it's a driver glitch, it's possible that it was an incompatibility with our specific system somehow, so we'll definitely be revisiting this in the future.

In the meantime, keep these issues in mind before you purchase.