You can create subwebs off the main site using the FrontPage server admin tool. Check out the relevant menu item in FrontPage to do that.
|In FP2002 it's under Tools > Server.|
|In FP2000 you just right-click the folder in the main web you want to make a subweb, and click create web. Then go to tools-security-permissions to set the author, administrator, etc...|