nimo codec should be taking care of yer problems.do not try the beta 9 or ull be sorry
when installing,choose xvid as well,and divx3.1, in the options.you could also update to the latest divx (from divx.com,freeware kinda ad suported )if it gives u an error like "xxx file is in use..bla BLA " reboot ,but before that stop every thing in ur startup,and try again.
add a couple 120mm fans overhead to drop temps by 10+ celsiusD.S.C-12(2)-
Utilize the following link, http://www.headbands.com/gspot/, download the program gspot. Open the avi file that you are not hearing the audio. This program will tell you what video and audio codec is being utilized by the avi file. You can the research and download the appropriate audio or video codec to get your avi file up and running.
I would stay away from nimo codec pack if i was you.Alot of codec packs cause problems.There ends up being conflicts between the codecs they install.As a matter of fact a few versions of nimo did this.Think one that I remember was ver.5.8.I always install my codecs individually and only what I need to avoid these conflicts.And as stated by others Gspot is a very good program to tell you what codecs are installed and what you need.