It’s likely just a few steps to make this happen:
1) Create a new template group under Templates. Don’t make the index template in this group your site’s homepage yet, but note this option for later.
2) Build the template files and links as necessary, as your homepage design likely has a different layout and content. Make sure these pages aren’t linked anywhere publicly yet until you’re ready, but you can still view them as a super admin for testing purposes. Test, test, test.
3) Once you’re ready to flip the switch, ensure all of the necessary weblog paths are set up under Admin > Weblog Administration > Weblog Management > (name of weblog) > Edit Preferences > Path Settings. Repeat this for all of the weblogs you’ve configured.
4) Finally, click the Templates tab in the main navigation and update the template group that you’d like to use as your homepage. To do this, check the box on (template group name) > Edit Group > Make the index template in this group your site’s home page? Now go to your website. Everything should jive.
That should be it. If it doesn’t work, let me know.
geof