When moving a page or even doing something as simple as changing its filename (and thus its URL), it's important to do it the right way. Done properly, you'll let search engines know where the new page is, and ultimately, even transfer the link love and other relevance weight to the new page.
What's the right way? Using a "301 redirect." Lisa Barone, over on the Bruce Clay blog, has an excellent post explaining How to Properly Implement a 301 Redirect. Today's Search Illustrated paints a graphic description of the process:
A 301 redirect is a command used to tell the search engines that a page has permanently moved, and that you want them to index the new page and drop the old one from their index. It’s basically a change of address card for the Web. As long as everything is done correctly, a 301 redirect will ensure that you keep the rankings earned by the old page and it will prevent the duplicate content nightmare that should arise if the engines were to index box version of your site.
How to Implement 301 Redirects Using .htaccess for Apache: To begin using the .htaccess file to redirect page(s) on your Web site, open up your FTP and login to your Web site. Work your way into in the root Web folder in order to access your .htaccess file. This little gem is the file you’ll need to edit. (A little piece of advice: The dot in .htaccess makes it a hidden file, so make sure your FTP browser is enabled to view hidden files. Otherwise you’ll never find it and your IT guy will laugh at you when you ask him for help.)
When you start editing the file, use a UNIX style text editor, not Notepad. Typically, an HTML editor or code editor such as TextPad works just fine. To 301 redirect pages using the .htaccess file, you will add a line to the file that will tell the server what to do. You can do this a couple of ways:
RedirectPermanent /old-file.html http://www.domain.com/new-file.html
Redirect 301 /old-file.html http://www.domain.com/new-file.html
A redirection from one domain to another would be:
RedirectPermanent / http://www.new-domain.com/