I am having this problem also. I have a 2005 instance and a 2008 instance and
am attempting to add a 2008 R2 instance on my Windows XP SP3 machine. I keep
getting the below error. Everything seems to install correctly except the
database engine.

Thanks,
Neal

2010-02-17 15:08:42 Slp: Sco: Attempting to get account sid for user account
NT AUTHORITY\NETWORK SERVICE
2010-02-17 15:08:42 Slp: Sco: Attempting to get sid for user account NT
AUTHORITY\NETWORK SERVICE
2010-02-17 15:08:42 Slp: Sco: GetSidForAccount normalized accountName NT
AUTHORITY\NETWORK SERVICE parameter to NT AUTHORITY\NETWORK SERVICE
2010-02-17 15:08:42 Slp: Sco.UserSecurity.NormalizeServiceAccount - Account
NT AUTHORITY\NETWORK SERVICE normalized to NT AUTHORITY\NETWORKSERVICE
2010-02-17 15:08:42 Slp: Sco: Attempting to get local system account name
2010-02-17 15:08:42 Slp: Sco: Attempting to get NT account from sid S-1-5-18
2010-02-17 15:08:42 Slp: Sco: Attempting to get account from sid S-1-5-18
2010-02-17 15:08:42 Slp: Sco: Attempting to open SC Manager
2010-02-17 15:08:42 Slp: Sco: Attempting to open service handle for service
MSSQLServerADHelper100
2010-02-17 15:08:42 Slp: Invoking ChangeServiceConfig Win32 API
2010-02-17 15:08:42 Slp: Sco: Attempting to close service handle for service
MSSQLServerADHelper100
2010-02-17 15:08:42 Slp: Sco: Attempting to close SC Manager
2010-02-17 15:08:42 Slp: Prompting user if they want to retry this action
due to the following failure:
2010-02-17 15:08:42 Slp: ----------------------------------------
2010-02-17 15:08:42 Slp: The following is an exception stack listing the
exceptions in outermost to innermost order
2010-02-17 15:08:42 Slp: Inner exceptions are being indented
2010-02-17 15:08:42 Slp:
2010-02-17 15:08:42 Slp: Exception type:
Microsoft.SqlServer.Configuration.Sco.ScoException
2010-02-17 15:08:42 Slp: Message:
2010-02-17 15:08:42 Slp: The account name is invalid or does not
exist, or the password is invalid for the account name specified.
2010-02-17 15:08:42 Slp:
2010-02-17 15:08:42 Slp: Data:
2010-02-17 15:08:42 Slp: WatsonData = MSSQLServerADHelper100@NT
AUTHORITY\NETWORK SERVICE
2010-02-17 15:08:42 Slp: DisableRetry = true
2010-02-17 15:08:42 Slp: Inner exception type:
System.ComponentModel.Win32Exception
2010-02-17 15:08:42 Slp: Message:
2010-02-17 15:08:42 Slp: The account name is invalid or does
not exist, or the password is invalid for the account name specified.
2010-02-17 15:08:42 Slp:
2010-02-17 15:08:42 Slp: Stack:
2010-02-17 15:08:42 Slp: at
Microsoft.SqlServer.Configuration.Sco.Service.Chan geServiceConfig(UInt32
dwServiceType, UInt32 dwStartType, UInt32 dwErrorControl, String
lpBinaryPathName, String lpLoadOrderGroup, String lpDependencies, String
lpServiceStartName, SqlSecureString lpPassword, String lpDisplayName)
2010-02-17 15:08:42 Slp: at
Microsoft.SqlServer.Configuration.Sco.Service.Chan geStartAccount(String
userName, SqlSecureString password, Boolean bAutoSetServiceLogonRight)
2010-02-17 15:08:42 Slp: ----------------------------------------