In Explorer or Netscape the thread "number" is atop the page you are viewing now. Simply highlight it, go to "edit" and select "copy" and then under edit again hit "paste" in your reply.
My computer knowledge level is 2 out a possible 1000, so if I can do it, it has got to be DEAD easy!
Here is one that features an interesting exchange with the poster above,
drtravels.
http://www.flyertalk.com/forum/Forum57/HTML/000794.html
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~ Glen ~