First, We will need to make sure your Windows Server 2008 is a clean install.
If you already have Microsoft SQL server express then you need to uninstalled it first.

Preparing Anything:

1. ISO Microsoft SQL Server 2005 full release (en_sql_2005_std_x86_dvd.iso)
2. Microsoft Service Pack (we can download it from :  http://www.microsoft.com/downloads/details.aspx?FamilyId=FB0EE17E-96EB-4CBB-AC09-95A4DCF73077)
3. Microsoft SQL Server 2005 SP2 (you can download it from microsoft website )