jdMorgan - 4:44 pm on Apr 7, 2010 (gmt 0)

You need two sitemaps, one for example.com at example.com/sitemap.xml, and another for subdomain.example.com at whatever location in the filesystem will be accessed when the URL subdomain.example.com/sitemap.xml is requested -- often at the "file location" example.com/subdomain/sitemap.xml if you use a control panel to set up the subdomain.

In the case of sitemap files, the search engines will treat subdomains as entirely-separate from the main domain, and not necessarily related in any way, and not necessarily even on the same server. Therefore, each of those two sitemaps must include only URLs referring to their own hostnames.

Jim