[support] Blogs and RSS feeds

[Roger]

We have Drupal 6.19 working with a highly modified theme, its basically
a data entry for calendars of events.
I have blog module turned off and RSS removed (Commented out) from the
page.tpl.php 

I've been asked to build a youth fourm on the site with Blog, and RSS
feeds.

Can a new application such as the youth forum use another theme in the
existing installation and have the desired modules without it affecting
the primary use of the site or would it be more desirable to use
multisite and start the youth forum in a new database/installation.

I hope I've expressed this right, I'm at a bit of a loss with
explanations.
thanks in advance
Roger