How do i backup the servers?

Our ABC Company has 25 clients PC connected to the below servers,

1) Domain Controller Server named ABCDC01 (MS Server 2003 Std Ed. SP2) 

2) Exchange Server 2007 named ABCEX01 (MS Server 2003 Std x64 Ed. SP2)

3) SQL Server 2005 (Microsoft Dynamics AX 2009) named applicationsrv (MS Server 2003 R2 Std Ed. SP2) 

I would like to know what is the better & easiest way to take backups for the all the above. please advice.

Thank you