Video files in x64

Hi, i recently upgrade my motherboard to a Gigabyte GA-K8N51GMF...

I used tie able to play video files, but most no longer work, if i try downloading a codec pack (e.g XVID) the media player only crash when i try to play them.....i am currently uses the latest nvidia video driver

also my cpu is AMD64 3200+

any ideas why this is happening?

Regardless of this thread being two years old with no replies, I figured I would try to clear things up with my own opinions: 

The codec packs themselves were designed to run in a 32-bit environment.. I have two work arounds for you (regardless of this thread being nearly 2 years old, lol).

1) Download and install VLC Media Player (videolan.org) - it will play virtually any video file (including Quicktime .mov files)

2) Where the codecs are designed for the 32-bit environment, you could always try enabling the 32-bit shell version of Windows x64 (switching between 32-bit and 64-bit shells).
Linkage: http://extended64.com/blogs/bhpaddock/archive/2005/05/22/539.aspx