i use shark007 codecs
never had any problem with them
very simple to use. it tells you when there is an update. just uninstall old one then install the new one and it works
you dont have to touch any settings
i used k-lite codec pack for quite a while before but it caused problems.
with shark007 i haven't had problems on mine or relatives pc's on windows xp,vista or windows 7 http://shark007.net/
install the normal version first then the x64 one after simple