All the information you need is available in the SAP notes and in this SAP note 1476239 - SAP system migration to Windows 2008/2008 R2
If you are planning to move to MSSQL 2008 then check this SAP note as well.
1152240 - Setting Up Microsoft SQL Server 2008 (R2)
It provides the kernel and SP level requirements.
There is an option to enable page compression in MSSQL. You can achieve this if you do a system copy using R3load export and import.
Good Luck
RB