Want Good Audio/Video Mixing/Editing Software Free..

Friends, I need a software for doinf following tasks..

1) I have collection of Instrumentals of Hindi songs on my PC.I wish to mix my friends voice with the instrumentals to check how does it sounds with instruments just for fun..

2) I wish to convert My original DVD which is in ".VOB" file format in to ".AVI" format
for saving of space on hard drive.

3) I also wish to Edit DVD and just take clip of songs to copy on my PC.


I have tried some Free softwares such as 1)Virtual Dub&2)AVid free DV
from Digit Free category but it could not serve my purpose.

can anybody suggest any Free/Trialversion software for doing above mentioned tasks combinedly or different softwares for above work..?

Thanks in advance..

-Mahesh