apache rewrite module

Does anyone know how to setup rewrite rules so that:

user1.mydomain.com is rewritten to /home/users/user1
user2.mydomain.com is rewritten to /home/users/user2

and

www.user1.mydomain.com is rewritten to /home/users/user1
www.user2.mydomain.com is rewritten to /home/users/user2

with user1.mydomain.com/something rewritten to /home/users/user1/something

If anyone has any pointers.

Thanks