You want to know the user’s Flash Player version.
Use a plugin-detection script that
runs in the browser before loading the Flash
Player, or use ActionScript
getVersion( ), or
within the Flash Player, as supported by the minimum Player version
you expect to encounter.
There are two broad categories of Flash Player version detection: you can attempt to detect the Player version with a browser-based script before the Player loads, or you can use ActionScript within the Flash Player to check the version that is currently running.
The problem with the first method is that it doesn’t work on all platforms and with all browsers, as explained in part at http://www.macromedia.com/support/flash/ts/documents/browser_support_matrix.htm.
Therefore, you should guard against a “false negative” in your detection approach; even if you fail to detect the Flash Player plugin, you should give the user the option of telling you that he has the plugin installed and would like to view your Flash content (i.e., don’t force visitors to the Macromedia Flash installation page just because you can’t detect their Player version).
There is a wealth of existing documentation on detecting the presence and version of the Flash Player plugin with a browser script, so refer to the following URLs for explanations and examples.
Macromedia Technote 14526, “How to detect the presence of the Flash Player,” is a good starting ...