Unless you have another Mac you could start this one in Target Disk Mode to, you'll need to obtain a retail copy. Currently the only OS that Apple offers via retail channels is Leopard; you may be able to locate a retail copy of Tiger through other sources (like eBay). Avoid purchasing "Install" or Restore" versions, they are machine type-specific.
Apple OS's are not available as downloads (not anywhere legally, anyway), and you'll need a functioning OS to boot this machine to, to determine the nature of the disk problem. Either via Tiger/Leopard CD/DVD or another Mac: those are the available choices.
It is possible--though very unlikely--the HDD in the laptop is disconnected. The iFixit guides are a good source for removal & replacement of drives. If you can hear or feel the drive spinning up when you power on the laptop, then that eliminates a disconnected drive.