Question : Problem: Slow HD Video Playback

My old PC is Intel 915GAV, 3.0 Dual core P4, 1GB DDR 400mhz

I picked up an Radeon HD 4550 card for it, in hopes that HD videos would run smoothly.

The videos  run in slow motion/skip as much with the onboard as they do with the new card.

So my next question is, which video players actually use the hardware for playback? Or did I just not get a powerful enough videocard?

The video players I use are VLC, Zoom, and KMplayer. Zoom works the best, although there's still a lot of slowdown with 1080p .mkv files.

Answer : Problem: Slow HD Video Playback

Is the problem specifically compressed HD video, like blu-ray or H.264?  That has higher requirements of your hardware, including your cpu.  You should be able to see if this is what is happening by looking at task manager and monitoring the cpu level.  You can run the diagnostic to see if your hardware is up to the task: http://www.cyberlink.com/stat/technology/enu/next-gen-disc-solution.jsp