A while back I installed SQL Server 2008 on a development machine which already had Sql Server 2005 express from Visual Studio. When I look in my programs, I see \'Microsoft Sql
If your using the SQL Server 2005 Configuration Manager you will only see 2005 instances and lower.
To view instances of SQL Server 2008 you will want to make sure you are using SQL Sever 2008 Configuration Manager.
The final option would be to View All services using the Service Control Manager. Here you will need to look at what instances of SQL Server you have running on the machine.