Unless you have some sort of troubleshooting product (like a TechTool Protogo from Micromat), unfortunately you absolutely must have the OS X install discs to fix this. You could buy new discs or borrow a friend's (you should check if that's legal first, but if you already rightfully own the same version of OS X that you are borrowing, it is unlikely to be a big deal).

If you are able to boot into single user mode (hold command-option-S at startup), you could try entering the command fsck -y to see if you can fix some disk errors (if there are any), but it is very unlikely (though not impossible) that this alone would get you up and running again.