Hello, I'm New here. Can you explain what a " beta " download is , why i should take it or not. I'm on Vista. Thanks for your help.

Beta is when I try new things on the game (new features, bugfixes) but want people to test it before releasing to the general public. Usually the beta after few days become the new version of the game. So you can download it only if you want to try the new features without waiting, or give feedback, otherwise you can just wait for the official announcement.

oh~I think windows XP and windows 7 are better than vista, I can play WoW and use wow helper-vcsale in my computer

I need to get a Pc with windows 7 myself too, to see how it is. Everyone I know talks well about 7, and I'm currently using Vista instead...