Oops sorry, for some reason I thought it was his work.
Thanks for your reply.
No, basically, because the main site is on subdomain1.domain.com when I create a second site, WP wants it to be subdomain2.subdomain1.domain.com so I edit the site to be subdomain2.domain.com and use the domain mapping tool to map the domain name to site id 2.
Am I doing it wrong?