Attach database failed for Server '{SERVER_NAME}\{INSTANCE_NAME}'. (Microsoft.SqlServer.Smo)
You need the "AdventureWorks2008R2_Log.ldf" file.  And put it in this folder:
"C:\Program Files\Microsoft SQL Server\MSSQL10.50.MSSQLSERVER\MSSQL\DATA\"

The easiest thing to do is download the "full backup" file from that site and then restore it, (instead of attaching.)