Yes, in Windows SharePoint Services Central Administration, under Virtual
Server Configuration, go to create  a top-level Web site:
Select the default web site (or other virtual  server) from the Virtual
Server List. This will bring up a page titled Windows SharePoint Services
- Create Top-level Web Site.
From here, at the Web Site Address option, click the radio button: Create
site at this URL: and leave the URL path defaulted to "root".

As to your Q2, yes you may create another virtual server  on the physical
server which hosts the portal (you do this via IIS + see the SPS Admin
guide).