As many as you like.
In fact I have 3, IE, Firefox and Chrome and I have all 3 open at the moment with no problems.
About your email address. I wouldn't post that in public forums like these as they can be farmed by bots for spam purpsoes. I have asked the Forum Admin to edit yours out.
Hi, I am a newbi, and I would like to know if it is okay to have two browsers installed. I have IE9 and Google Chrome. I only use IE9.
Note: This post was edited by a forum moderator to remove exposed email address on 02/22/2012 at 6:07 AM PT