Apache Rewrite question

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I'm certainly no expert at this, but I'm assuming the following is
possible...but as a beginner, I have no idea where to begin!

I'm taking over a site, and the powers that be would like to keep the
status quo (http://original.com , for the sake of clarity).

They've recently purchased http://newsite.com , and would like to be
able to edit the files through the main CMS (CMS Made Simple is what
they're using), the one that controls http://original.com .

Adding those files in isn't a problem, except for the URL in the
address bar. Normal pages in original.com display as such:

Anything I add to the CMS will display in this way, so I CAN'T simply
add in the newsite.com pages in a subdirectory /newsite/ and use:

RewriteEngine On
Options +FollowSymlinks
RewriteBase /

RewriteCond % newsite.com
RewriteCond % !/newsite
RewriteRule ^(.*)$ newsite/$1 [L]

Does anyone know a way to redirect http://newsite.com to
http://original.com/index.php?page=newsite without affecting all the
other pages in the site?

http://newsite.com will only have two or three pages, max, so I can
use the same method to mask the other two or three URLs.

This seems possible, if not easy and possible, but my Googling has
been in vain. Thoughts? TIA, Kate

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