How do I read avi and mpeg files on programs like Shareaza, Limewire, and Bittorent if my computer plays mpg?

i have shareaza, limewire, and bittorent, and in all of them i can't read avi or wma or mpeg files. my laptop only reads mpg...Also---on shareaza, how come the volume doesn't work, or is that just the stupid vidsi load? Plese help, and thanx for anything or any info!!!!