form resubmit: how to ignore second request? (if 1 second after the first one)

I have a form that is occasionally getting submitted twice when only once is intended (some user's combinations of typing, hitting enter, clicking submit, hitting enter twice, etc.).  Is there an easy way to catch this on the server, and get it to just ignore processing of the second request, but still let the first request complete?

If it matters, I've traced it enough on the server to verify that when the requests are right behind each other like this, the second one is handled in a separate thread from the first one.

Thanks for any help-

ASP.NET 2.0
...