no-www CNAME in windows DNS

I've asked the sysadmin of a client of mine (runs windows) to create the following CNAME records for their new website:

www.example.com CNAME foobar-web-server.com
example.com     CNAME foobar-web-server.com

The problem is that he cannot create the second entry. I know how this is possible in Linux with bind, by using an ending dot on the alias, but how is it possible in windows DNS?

I guess what he sees looks like:
_{(source: iisanswers.com)}

He tells me that leaving the "Alias name" blank gives him an error.

Any ideas?

thanks

You don't say what the error is, but it is probably correct. The root of the domain will have at least SOA and NS records (and possibly MX and A records too). DNS doesn't allow a CNAME to coexist with other records. See RFC 1034 section 3.6.2:

If a CNAME RR is present at a node, no other data should be present; this ensures that the data for a canonical name and its aliases cannot be different.

RFC 1912 section 2.4 has some further examples:

A CNAME record is not allowed to coexist with any other data. In other words, if suzy.podunk.xx is an alias for sue.podunk.xx, you can't also have an MX record for suzy.podunk.edu, or an A record, or even a TXT record.

You will have to use an A record for example.com instead of the CNAME.