I am using Apache2.2 on the Windows XP with php5, I have no problem to get the access to http://www.mysite.com, now I want to add a sub domain, looks like http://subdomain.mysite.com. I don't know how to configure this in the Apache. Thanks for any help!
How to create a sub domain under Apache
Look up named virtual hosts. If you get stuck, post back.
You will need to set up a DNS entry in your DNS server. If this is managed by a hosting provider, contact them to find out how.
Once you've got the DNS set up, look up named virtual hosts as Sxooter says.
They aren't really sub-domains at all. Rather, they're just an extra "A" record in an existing domain (you could set one up as a true subdomain, but nobody ever actually does, nor do they need to).
Mark