To remove all known instances of SQL Server, follow these steps:
1. Locate, and then delete the %drive%:\Program Files\Microsoft SQL Server\MSSQL\Binn folder.
2. Locate, and then delete these registry keys:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\MSSQLServer
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server
3. Locate, and then delete these registry keys:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSSQLServer
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\SQLSERVERAGENT
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSSQLServerADHelper
4. The three registry keys in step 3 correspond to the default instance of Microsoft SQL Server 2000. Named instances appear similar to those listed in step 3, along with $instance_name, because instance_name is the name given to your particular instance. After you locate the correct keys for the instance you are removing, select those keys, and then delete them.
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSSQLServer$InstanceName
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\SQLSERVERAGENT$InstanceName
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSSQLServerADHelper$InstanceName
Let me know if this help ...
Thanks
J. Kusch