It's been a week since I've installed MOSS on our development server and found out that it's quite easy to install and configure except for changing the email of users associated in MOSS. I've done some research and here is it:

1) Go to Sharepoint Server (physical server), Click Start -> Microsoft Office Server -> Sharepoint 3.0 Central Administration.

2) Login as administrator, on the left pane click Shared Services Administration.

3) Click the default Shared Services by default it's SharedServices1. Login as administrator.

4) Click user profiles and properties.

5) Click view user profiles.

6) User list is displayed. To edit the email address click the dropdown menu and select edit.

Note:

When adding user to group or site just click the address book popup to browse to the list of users (email address can be seen in this list) .