Yes you can, by using a content editor web part, another web part (can't remember the name but someone will help me) that can tell you the ID of the portion you want to hide  by displaying it as you mouse over it, and a little bit of javascript.

You find out the ID for the portion your wanting to hide, then you write a line of JavaScript to hide that portion and put it in a Content Editor web part that's hidden on the page. The nice thing about this is it doesn't require editing the page itself, and if you want to restore it you can just remove the content editor wp with your javascript, or comment the javascript out and everythings back to normal.

If someone doesn't post the details, once I get to work I'll follow up with them.

mindsharpblogs.com/.../801.aspx wil do it.

Very timely subject. I wrote a document discribing this and other
tricks that you can do with the CEWP. If you would like a copy of
the document feel free to email me or grab it at my site.
http://bobfox.net/spnj or http://bobfox.net/spblog

As a side note as well, if you hide  or remove your Topics area/subweb, the portal  home page will show your top areas in the left nav as opposed to the subareas under Topics.

Enter the following into a CEWP (from memory):

<style>
.ms-nav
{
Display: none;
}
</style>

Be aware, you will lose the bread crumb at the top of the left nav and
the Edit Page link at the bottom of the Actions. There are other ways
(perhaps better ways) you can accomplish this if you have access to the
direct mode pages.