Burning Movies stored on External HD= Problems

I am having two possibly related computer troubles.

My first trouble is my graphics card. When I try to watch a movie or video file using any playback program, my computer will completely freeze or the graphics card stops working and my screen becomes all blocky and really huge graphics with limited color display. It causes pictures to look like a bunch of huge pixels. When I completely disable graphics acceleration,I can watch movies with no system freeze up, but then I cant play games.

My second problem is My external HD: I used to be able to do anything while burning a movie from it. Now if I try to do anything while burning the computer completely freezes up and the disc is ruined. If I burn from the internal Hd I can do anything while I burn.

Dvds rip to it perfectly with no snags no matter what Im doing.

Both occurences involve the same type of freeze up. Are these problems related? What is behind each of these problems?

My computer is a Toshiba S206 2.8 GHZ Win Xp SP2 (all current updates) with 896 mb Ram and a Nec6500A burner using stock firmware. It has a ATI Mobility Radeon 9000 IGP Graphics card with 128 mb of shared video ram. The external harddrive is connected via firewire through a Zonenet PC Card to a Western Digital 320GB 7200 Rpm Hd with 8 Mb Cache. I use dvd decrypter to burn. ( I tried running dvd decryptor installed off the external Hd and I have the same freeze up problem)

Thank You for your help!!!