Windows XP home in a Domain

As the heading describes is it possible to do that? I came into a questionable state where one of the offices is running windows 2003 standard server and they are connecting to that domain through windows XP Home machines and access the exchange server over there. SO just wondering how'd they do that? I advised them to get windows XP pro to one machine to get connected to that server. Another guy came and configured new machine to that network using windows XP Home. Can anyone explain how come this is possible?

The option to join a domain is not available on an xp machine, but here are TWO alternatives:

NOTE:
Windows XP Home Edition is not designed to join domains; only workgroups.

#1:
Visit http://vowe.net/archives/001639.html and download the free and widely available Xteq X-Setup 6.1 utility. You can then join domains with WinXP Home Edition.

#2
1. Log into XP Home using a local computer account that does not have a password.
2. Open My Computer, click the Tools menu, then click Map Network Drive.
3. Select a folder on your network by clicking on the Browse button.
4. After selecting the folder, click on the different user name link on the page.
5. In the Connect As dialog box, for user name enter domainx\user (where domainx is the domain you want to connect to).
6. Enter your domain user password and then click OK.
7. Check the Reconnect at login box and press Finish.
8. Now when you start up the computer go to My Computer and double click on the networked drive. This will cause XP to send the credentials to the Domain and allows you to access the drive.
9. Now you can access files and folders throughout the domain without having to your user name and password.

This info was found: http://www.staffkit.com/resources/join_domain_windows_xp_home.htm