Found Answer.......!!!!!!!
Officially Microsoft Office 2003 Interop is not supported on Windows server 2008 by Microsoft.
But after a lot of permutations & combinations with the code and search, we came across one solution which works for our scenario.
The solution is to plug the difference between the way Windows 2003 and 2008 maintains its folder structure, because Office Interop depends on the desktop folder for file open/save intermediately. The 2003 system houses the desktop folder under systemprofile which is absent in 2008.
So when we create this folder on 2008 under the respective hierarchy as indicated below; the office Interop is able to save the file as required. This Desktop folder is required to be created under
C:\Windows\System32\config\systemprofile
AND
C:\Windows\SysWOW64\config\systemprofile
This worked for me...
Also do check if .NET 1.1 is installed because its needed by Interop and ot preinstalled by Windows Server 2008
Or you can also Use SaveCopyas() method ist just take onargument as filename string)
Thanks Guys..!