HDTV Displaying on PC Monitor

Hi, guys!
I have a PC with a Radeon X550 Video Adapter and I recently
downloaded an HDTV movie with 1280x720 video size with approximately 5Mbps video bitrate.
So the video looks totally serene when you’re watching people’s faces and light stuff but when you’re watching scenes with dark background it seems kind of dusty. I am using the new BSPlayer (with K-Lite 3.9.0 mega) because the KM Player gave me hard time with the sound and picture synchronization.
So is my problem the hardware or the software?

Try with VLC:

http://www.videolan.org/vlc/

If that doesn’t work, try GOM player:

My machine with a Radeon works better with GOM while I get better results with VLC with the GeForce.

Hi, Dalen Quaice. The GOM Player also slows down the picture and
shows a little dusty background.
The same goes for VLC. Maybe my video is a little slow. Only 256MB?
Huh?

Yes, likely you need a better video card.

What’s the rest of the computer? Does it share Video memory? Is it a laptop? What size is the processor and how much Ram do you have? I have a Radeon X800 256 AGP Pro and it plays HD fine.

Well, I have an AMD Athlon 64 3200+ working at 2.01 GHz;
2 GB of RAM and ATI Radeon X550 (RV370) (Asus EAX550) Video Adapter.
So if I should upgrade to something better I’m open to recommendations.