I've got a website (www.centreholidays.com) and we have 100 or so employees which we have assigned subdomain addresses to (Eg. www.billd.centreholidays.com).

The information that shows up on the agent (subdomain) site is exactly the same as the primary website except that the contact info / intro image change. Ths information is pulled from a database.

The problem I face is that we want these sub-domains to get found on the web when you do a search in google etc. What can I do to get these sites seen as separte entities?

Any help would be appreciated.

first of all make your subdomains bill.atyourcompany.com dropping the www
this should point to a separate folder on the root directory. If your root folder is /public_html/ then the new subdomain folder is /public_html/bill
In the bill folder should be an index.htm or index.php depending on your db and the index page should be totally different from the main site index.

as far as I know google takes subdomains as separate sites by default. however you still will have to make these subdomain pages unique.