Who among you is bold enough to tackle this URL rewrite question?

Hi,

I'm using Apache 2 running on Linux. I have a question about
rewriting URLs using an .htaccess file. I have several domains
(mydomain1.com, mydomain2.com, mydomain3.com) pointing to the same
IP. How would I construct a rewrite rule such that if someone visited
the URL

http://otherdomain.com/mypage.html

where "otherdomain.com" is anything other than " mydomain1.com", the
URL would be rewritten as

http://mydomain1.com/mypage.html

I only want the rule to be in effect for the page, "mypage.html". How
would I construct such a rewrite rule?

Thanks, - Dave