Redirect non www requests without redirecting sub-domains

To replace a legacy web site, a client has pointed their DNS at my server where a new version of the website exists.

However they still serve http://support.example.com from their own server.

I have noticed that non-www requests, e.g. http://example.com still point to their own server, therefore show the old web site.

How can I point non-www requests, http://example.com at my server without breaking the functionality of their 'support' sub-domain?

• The client's server is a Microsoft server, mine is Linux/Apache
• Edit: Changing the DNS 'A' record will not break the existing sub-domain
• I know I could add an index.html page to the front of the old site, but if it was ever deleted the page requests would cease to work
• I can't use mod-rewrite because I don't have access to their web server files

PROPOSED SOLUTION:

On the client DNS, create an A record for:

• support.example.com – IP of the cl开发者_高级运维ient's server
• example.com – IP of my server
• www.example.com - IP of my server

No need for any DNS changes on my server regarding this domain

Changing the A record for example.com won't affect the A record for support.example.com.