If you load SP2 for SQL 2005 or an update to SP2 for SQL 2005 and then SQL will not start and you get an error that says a database file is corrupt and needs to be restored from backup here's what you do to fix it.
1. Locate the SQL error log and see what file was not opening. For me it was mssqlsystemresource.ldf and I suspect it will be the same for you.
2. Search your server for mssqlsystemresource.ldf and you will find 2 of them. It's likely that one will have an mssqlsystemresource.mdf in the same directory and the other will not.
3. Replace the one in the path that was in the error log with the other one. In my case I replaced the ldf that was in the directory without a matching mdf with the other ldf.
4.. Voila, SQL will start now.
If you need anyting more detailed than this I am sorry because I am not really a SQL expert.