ok I'm going to avoid the rant that I would usually go off on where I hee and haw about coding cross-browser compliant HTML, and explain that even with a redirect there are several other browser on the market besides the big two.
Also I'm going to assume that you do not want to actually open one browser from another, you just want to send the user to the netscape or IE version of the page, right?
if you are using CGI.pm look up user_agent()and redirect() in perldoc CGI