How To Detect Specific Browser And Then Redirect

Basically, I need a browser detection script that will detect what version of what browser the user is reading. My site works with IE 5.5SP2 and up, Netscape 7.2 and up, Opera 7.1 and up, and Firefox 1.0 and up (have not tested on any Mac browsers).

What I want the script to do is once it's detected a version of one of these browsers or higher, to continue loading the page. If it detects a lower version, or any other browser, I want it to direct users to a page telling them they are using an old or untested browser, where I have links to update the tested browsers and a link to continue to the site anyways

I have tried a couple scripts, but they only partially work. The one below seems to work so far for the two browsers I can test on (It goes to the good page for IE 6 and the bad page for NS 4.79 (I added Firefox and Opera myself, so I don't know if it works).

browser = navigator.appName
ver = navigator.appVersion
version = ver.substring(0,1)
if (browser=="Internet Explorer") {
if (version<="5.5")
document.location.href="index2.html"
}
if (browser=="Netscape") {
if (version<="7.2")
document.location.href="index2.html"
}
if (browser=="Firefox") {
if (version<="1.0")
document.location.href="index2.html"
}
if (browser=="Opera") {
if (version<="7.1")
document.location.href="index2.html"
}

How do I specify that IE 5.5 has to be 5.5 SP2? And how do I specify that every other browser in the universe except those lined out above in the code has to go to index2.html? I don't know how to specify that Safari has to go to index2.html while Netscape 8 doesn't.