Do you have a backup of the Exchange Information Store, done using the Exchange Agent? If so, then it should be fairly straightforward.
You should restore the filesystem that got corrupted, then using the Exchange System Manager, mark the database as overwritable by a restore. Then restore the information store.
The Exchange restore section is covered in the Administrator's Guide page 1258 onwards.
If you haven't been backing up using the Exchange Agent then you may have a bigger problem...