ati 2600XT sometimes video shifting lower part of screen

Help, I have ATI 2600XT 256mb on my Dell 531 AMD 5000 X2 2GB playing AVI video file from WD 500gb external hard drive on my Sony 720p 46" LCD. Here is the problem that sometimes on the lower part LCD screen video is shifting for few seconds. Does anyone is having problem with this?

Update: I went into ATI to control with video resolution and changed to 1280x720 with 60Hz refresh. This will get rid the shifting image (was on and off). If I keep 1360x768 with 30iHz (I guess i is stand for interpolation) my problem re-appear again, but at this resolution my video is smooth. Only the problem that at both resolution above, I am having the ghost image. I don't know what to do and don't think this is my Sony LCD television because the on board video is working fine (Dell 531).
I am wonder any one out there is having the same problem as I have.

Just update, I changed the resolution of the ATI Radeon 2600xt 256MB to 1920x1080 and my Sony 720P (1360x768) 46" KDL46S2010 is working perfectly. I don't understand why it work with this resolution because this LCD is 720p and 1360x768 max!!!
No more split or shifting on the lower screen or ghostly image.
I was given up the problem and bought Gigabyte GeForce 8600 GT 512MB and wait it to come in next week. Now I have to live with a spare card.