Dear Surojit,
SAP R/3 4.7c not work on windows 2008 & SAP ERP 6 EHP 6 not work on windows 2003.
So you have to update first to SAP ERP 6 EHP 5 with windows 2003 and sql 2005
Then upgrade windows to 2008 and sql to 2008
Then upgrade to SAP ERP 6 EHP 6.
You don't have to make system copy if you want to upgrade in-place upgrade.