[support] Can I Use a Slightly Modified Theme on Only One Page???

[Big Brother]

Hi Everyone,

My boss has a special request of me. We want to make a "sub-site" of
the current site we are running, which is:

http://narcosphere.narconews.com

I need to build a sub-site which will use most of the current theme
but with about 15-20% of changes. For instance, I am going to need to
change the banner for this "sub-site", get rid of the left column, and
change what's on the right-sidebar.

Is there an easy way to do this without having to make a whole new
drupal installation just for this sub-site?

If this isn't clear enough, please let me know and I can further
explain what I'm trying to do.

Thanks!

David B.