Repair a SQL Server 2000 MDF file
The fastest, simplest solution is to restore your last good backup. If that isn't an option you can try a workaround to make MSSQL think the database already exists:

http://sqlskills.com/BLOGS/PAUL/post/Disaster-recovery-101-hack-attach-a-damaged-database.aspx

Then you can run DBCC and see if it can repair the database, but even in that case you may still have data loss. You could also call Microsoft (maybe you already have a support contract), but the bottom line is that if you have a damaged database and no backup then there's not much that anyone can do.