The Notebook Review forums were hosted by TechTarget, who shut down them down on January 31, 2022. This static read-only archive was pulled by NBR forum users between January 20 and January 31, 2022, in an effort to make sure that the valuable technical information that had been posted on the forums is preserved. For current discussions, many NBR forum users moved over to NotebookTalk.net after the shutdown.
You need to be a bit more specific. Encoding/decoding? What resolution? What bitrate? What container? What player?
For sake of comparison, I was able to play (barely) 720P *.mkv files (h264 video/AC3 audio) on my T40 (1.5GHz Pentium M). This pushed my system to the limit however, dropped battery life substantially, and was only really stable when I used the CoreAVC codec and Media Player Classic (VLC was too slow for 720P h.264 on my machine).
If you truly want reliable playback of h.264 videos, you will need a computer with a graphics card that can accelerate h.264 decoding. Most newer graphics cards (including the integrated GMA4500 in all montevina chipset Thinkpads) can do this. This will offload most of the decoding to the GPU, and allow the CPU to throttle down. Because of this, 6 hours+ of 720P h.264 playback is possible on the x200(s/t) as the processor can drop to the lowest speed (800 MHz per core). You will be lucky to break 2 hours of battery life on the T43 for this (although if you are plugged in battery life is irrelevant).
Problems? See this thread at archive.org.
