SQL Server 2005 doesn't recommend using REPAIR_FAST... I removed the REPAIR_FAST functionality when I rewrote DBCC CHECKDB for SS2005. If you look in Books Online you'll see that the option is only there now for back-compat and doesn't do anything.
Before doing any repair you should use the option to restore from your backups...
Paul Randal
CEO, SQLskills.com: Check out SQLskills online training!
Blog:www.SQLskills.com/blogs/paul Twitter: @PaulRandal
SQL MVP, Microsoft RD, Contributing Editor of TechNet Magazine
Author of DBCC CHECKDB/repair (and other Storage Engine) code of SQL Server 2005