Have a look at this.

http://blog.sqlauthority.com/2012/05/05/sql-server-migrate-a-sql-server-reports-from-one-server-to-another-server/

Here is a another option that I have personally used for migrating from 2005 to 2008 R2

http://thandor.net/article/28 -Look for the RSScripter.zip link to download.