How did you delete it? It's not like it is some file somewhere easily accessible that it can be accidentally deleted. Depending on what you did, restoring the boot sector may not help.
It depends on your OS. In Server 2003, you need to boot to the Recovery Console and run the following commands:
If you are using 2008+, you boot to the Recovery Environment and run the following commands:
bootrec /fixbootbootrec /fixmbr
Again, this may not be all you need to fix your issue.