You would be looking at customizing the masterpage to accomplish this. 

In 2010 (You didn't have a version specified though 2007 / WSS should be similar) you can update the following lines to behave how you would like, or more specifically you could set the NavigateUrl of the SPLinkButton to whatever you want it to be if you only wanted to change the page that clicking the image navigates to.

&lt;td class="s4-titlelogo"&gt;
    &lt;SharePoint:SPLinkButton runat="server" NavigateUrl="~site/" id="onetidProjectPropertyTitleGraphic"&gt;
        &lt;SharePoint:SiteLogoImage name="onetidHeadbnnr0" id="onetidHeadbnnr2" LogoImageUrl="/_layouts/images/siteIcon.png" runat="server"/&gt;
    &lt;/SharePoint:SPLinkButton&gt;
&lt;/td&gt;


Redirect a subsite home link to the root site collection home page
Suppose you're some sort of crazy nerd fellow and you live in an area that's absolutely covered in fiber optics and network facilities. What kind of cost / infrastructure would be needed to hook in somewhere and get you're internet connection directly from a local datacenter?
