How have you backed up your SQL server data? did you run a DTS job on the SQL databases and then backup those files?
I've not used Arcserve 2000 yet in any anger, so am unsure whether it allows you to backup a database direct from the app itself..
If not, just put your tape in, go to restore, restore the Database backup file in question and then do a normal SQL restore... should work fine. (thats how I do it anyway.)