Hello,
Try adding the group SQLServer2005SQLBrowserUser$SERVERNAME and make it a member of administrators.
If you are trying to install SQL Server 2005 on a domain controller, then read the following article (Problem 4):
http://support.microsoft.com/kb/936302
For more information about user groups created by SQL Server Setup, please see the following article:
http://msdn.microsoft.com/en-us/library/ms143504.aspx
Hope this helps.
Regards,
Alberto Morillo
SQLCoffee.com