Wordpress Multisite and domain mapping

[#1]

Can't seem to get Wordpress Multisite to work on the new ccgi server, when i create a new subsite and try and get into dashboard it says Server not found
Firefox can't find the server at theflowerschool.ccgi.lesleya.plus.com. Would I be better going for seperate installs of Wordpress and create a database for each site.
I have the following DNS records set up at 123REG for www.theflowerschool.co.uk
* A 91.136.8.9        
@ A 91.136.8.9        
@ MX 10 mx0.123-reg.co.uk.        
@ MX 20 mx1.123-reg.co.uk.        
www CNAME ccgi.lesleya.plus.com.
Thanks

[#2]

I've not got much experience with mutisite however this is never going to work:

theflowerschool.ccgi.lesleya.plus.com

Because the domain doesn't exist in DNS.
If I was to set up multiple Wordpress sites, I'd install two instances in different folders and point each domain to its own folder.

[#3]

Thanks Bob, figured I was going to have to do that as not sure if domain mapping and subdomains will work on the new ccgi hosting, I think it was coming up with theflowerschool.ccgi.lesleya.plus.com as the domain mapping plugin within wordpress wasn't working as it should have been theflowerschool.co.uk
I've set up multisite before elsewhere but was having difficulty with this.
Do you need to do anything at your end to map the domains or can I just change the DNS records at 123REG to point to ccgi.lesleya.plus.com.

[#4]

If it's a new domain/sub-domain that you're wanting to point at the CGI platform then we'll need to associate it with your hosting account. Raise a support ticket and we can get that done for you.