Problem With SSMA for Oracle - Installation and Migration process

I have installed MSMA 2008 for Oracle with the following 2 installers

1. SSMA 2008 for Oracle.4.0.Install
2. SSMA 2008 for Oracle Extension Pack.4.0.Install

While installing the second one its giving an error like "you need sql server 2008 instance to install utilities database scripts" though Windows SQL Server 2008 is installed and running properly on the machine properly.

I am using WIN2008-SERVER\SQLEXPRESS ( Windows Authentication )  as a server name and if I bypass this and try connect SQL Server from SSMA , Its throwing an error called  "This version of the SQL Server is not supported. You must connect to an instance of SQL Server 2008."

I would like to know what went wrong and whether any further configuration is required.