Personally, I don't like that you can execute code in the address bar of any browser: I think it is a potential security risk. But, if you are on the phone to a custard (a cross between a customer and a b@stard), then this is a simple method that even a pretty non-technical person can cope with!
The only other ways I know of for a user to check what versions (if any) are installed on a machine are to look in the registry (and some people should not be allowed near Regedit), or to check for a folder called "Microsoft.NET\Framework\
" under the main Windows
directory (which may not be available to all users) and see what sub-directories exist. Since this means them looking into the Windows directory, I don't like to go there either - the damage a "non-technical person" can do without thinking is quite staggering, sometimes.
This method can be used very easily over the phone, and requires nothing that (probably) isn't installed already: Internet Explorer (it definitely doesn't work in Chrome, and probably won't in Firefox.)
Bring up Internet Explorer and paste into the address bar (note the upper- and lower-case, it is important):
You will get a popup saying something along the lines of:
Mozilla/4.0 (compatible; MSIE8.0; Windows NT 5.1; Trident/4.0;
Followed by a number of ".NET CLR" versions. All the user has to do is read out the message box content.