How do I restore a database on sql server through the command prompt?

Well, I figured out how to do it:

The command prompt is run like this:
"C:\Program Files\Microsoft SQL Server\80\Tools\Binn\OSQL.EXE" -E

Then write these lines to restore the database:
restore database mydbname from DISK = 'C:\xxx\xxx\xxx' with move 'database_Data' to 'C:\Database\xxx\database_Data.mdf', move 'database_Log' to 'C:\Database\xxx\database_Log.LDF'
go

It was the "WITH MOVE" that gave me problems. If you're restoring on another machine that doesn't have the exact same directory structure, then you need to add that.