htaccess troubles

I had this in my htaccess file:
RewriteCond %{HTTP_HOST} ^mydomain.com$ [NC]
RewriteRule ^(.*)$ http://www.mydomain.com/ [R=301,L]

Its purpose was to direct any calls for my homepage that were without the "www" to the "www" version, so there would be no more canonical domain issues with Google and the like. Unfortunately, I had to remove these lines in order to be able to access my Zen cart administration panel.

I have all of the Zen files in a folder called "catalog" located in my public_html area.

So might solve the canonical domain issue and still allow me to be able to get into the control panel? Please keep in mind that I only have a vague understanding of htaccess and mod rewrite.

Thank you,
GrandmaJ

P.S. I'm sorry, I forgot to add that the htaccess file in question is also located in the public_html folder and is used to also control hotlinking, "bad" spiders, and the like.

I'm sorry, I mis-typed in the above post. I meant to ask What alterations do I need to make to the htaccess file that will allow me to access the Zen Admin panel, but still solve the canonical domain issue? Sorry for the misunderstanding.

Grandma J