Cautious 301 Redirect for old domain name and links

[pcunite]

I have for the past several years had two domains pointing to the same hosting account. I would now like to drop one of these domain names. Also we are changing a few important links as well. So what I have is this.

Domain changes:
DomainOne.com - shutting down public access
DomainTwo.com - keeping

Link changes:
DomainTwo.com/pages/mypage.html >>> DomainTwo.com/pages/mypage2.html

Scary stuff:
Google has this page ranked pretty high:
DomainOne.com/pages/mypage.html

What is the best way to do this using only an .htaccess file?