Cannot connect to PC\SQLEXPRESS

hi All,
I am using Window 7 32bit OS With .........
1. Vs2008 with SQL Server 2005 (MSS Mangement Studio Express)  And
2. VS2010 with SQL Server 2008 R2 (MSS Mangement Studio).
I  installed both of setup in my PC. i have access both of sql server 2005 and 2008. but right now i have  access only sql server 2008 R2.
i am getting error for access sql server 2005 is mention below ....
"Cannot connect to PC\SQLEXPRESS Additonal Informaiton This version of microsoft Sql Server Management Studio Express can only be used to connect to SQL server 2000 and Sql Server 2005 servers.(Microsoft.SqlServer.Express.ConnecitonDlg)".
I am facing problem in connection string for 'attachdbfile' in Sql Server 2008 R2.
this connection string is working only SqlExpress in SqlSever 2005.
<add key="ConnectionString" value ="Data Source=.\SQLEXPRESS;AttachDBFileName=|D ...