NIS vs. AVIs & WMVs

I have read that other prople's AVIs and WMVs can contain dangerous code, executed when they are used.

(1) Is this true?

(2) If they can be dangerous, does NIS sufficiently protect against this kind of damage?

 

Currently, I am running NIS 2006 on Win2000 for a short while longer, and NIS 2010 on XP and Vista.

 

Thanks,

RickK