I ran across this on a website I hit this morning and found it to be quite useful. So I am reposting it here in case anyone else is trying to do this. In a nutshell, this bit of javascript will return a decimal value of the highest version of the Flash Player installed on an end users system. You can even specify the minimum version you are looking for and get a boolean TRUE or FALSE in return. Very slick.

// If called with no parameters this function returns a floating point value
// which should be the version of the Flash Player or 0.0
// ex: Flash Player 7r14 returns 7.14
// If called with reqMajorVer, reqMinorVer, reqRevision returns true if that version or greater is available
function DetectFlashVer(reqMajorVer, reqMinorVer, reqRevision)
{
reqVer = parseFloat(reqMajorVer + "." + reqRevision);
// loop backwards through the versions until we find the newest version
for (i=25;i>0;i--) {
if (isIE && isWin && !isOpera) {
versionStr = VBGetSwfVer(i);
} else {
versionStr = JSGetSwfVer(i);
}
if (versionStr == -1 ) {
return false;
} else if (versionStr != 0) {
if(isIE && isWin && !isOpera) {
tempArray         = versionStr.split(" ");
tempString        = tempArray[1];
versionArray      = tempString .split(",");
} else {
versionArray      = versionStr.split(".");
}
versionMajor      = versionArray[0];
versionMinor      = versionArray[1];
versionRevision   = versionArray[2];

versionString     = versionMajor + "." + versionRevision;   // 7.0r24 == 7.24
versionNum        = parseFloat(versionString);
// is the major.revision >= requested major.revision AND the minor version >= requested minor
if ( (versionMajor > reqMajorVer) && (versionNum >= reqVer) ) {
return true;
} else {
return ((versionNum >= reqVer && versionMinor >= reqMinorVer) ? true : false );
}
}
}
return (reqVer ? false : 0.0);

}