MU_Engineer :
The HD 2400 accelerates MPEG-2, H.264/AVC, and VC-1 on Windows. I don't know much about MKV, so I can't tell you if it accelerates that or not.
I know this is an old thread, but I have some info on that HD2400 card......Well not really info, but speculation. Over at the Visiontek boards, people are saying that the PCI version of the HD2400 doesn't actually have h.264 encoding. Everywhere I have read, it says it does, and I own the card, but haven't been able to test it yet. However, Visionteks support hasn't gotten back to me yet with the question. If they do I will post.