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 you want to find all the instance names, one way is to run powershell and execute the following
PS C:\> gwmi win32_service -filter "name like 'MSSQL%'" | fl DisplayName, pathname
For me the result is
DisplayName : SQL Server (SQLEXPRESS)
pathname : "c:\Program Files\Microsoft SQL Server\MSSQL10.SQLEXPRESS\MSSQL\B
inn\sqlservr.exe" -sSQLEXPRESS
DisplayName : SQL Server (SQLEXPRESS2005)
pathname : "c:\Program Files\Microsoft SQL Server\MSSQL.2\MSSQL\Binn\sqlserv
r.exe" -sSQLEXPRESS2005
DisplayName : SQL Full-text Filter Daemon Launcher (MSSQLSERVER)
pathname : "C:\Program Files\Microsoft SQL Server\MSSQL10.MSSQLSERVER\MSSQL\
Binn\fdlauncher.exe" -s MSSQL10.MSSQLSERVER
DisplayName : SQL Server (MSSQLSERVER)
pathname : "C:\Program Files\Microsoft SQL Server\MSSQL10.MSSQLSERVER\MSSQL\
Binn\sqlservr.exe" -sMSSQLSERVER
DisplayName : SQL Server Active Directory Helper
pathname : "c:\Program Files\Microsoft SQL Server\90\Shared\sqladhlp90.exe"
DisplayName : SQL Active Directory Helper Service
pathname : "C:\Program Files\Microsoft SQL Server\100\Shared\SQLADHLP.EXE"
DisplayName : SQL Server Analysis Services (MSSQLSERVER)
pathname : "C:\Program Files\Microsoft SQL Server\MSAS10.MSSQLSERVER\OLAP\bi
n\msmdsrv.exe" -s "C:\Program Files\Microsoft SQL Server\MSAS10.M
SSQLSERVER\OLAP\Config"
Look for the one that has MSSQL10 and make sure that the service is started. Then use that instance name when connecting via SSMS.
If for some reason you didn't install into the default structure you can always visit the Exe directly and check its version for something like 2007.100.xxx
I happen to have 2005 and 2008 express as well as 2008 standard
If I was better at PowerShell I would have piped the PathName to get the version info