DiskWarrior may be able to repair catalog damage that is keeping your hard drive from being used -- as long as the problem isn't physical damage of the drive. DW is a one trick pony, but it does that trick very well.
This is an excellent time to get an external hard drive for backup. It will cost you between $90 and $200 depending how large a drive you choose. A Firewire drive would be a bit better than a USB drive. **Every laptop owner should have a bootable external drive and should use it religiously for backup ** given that laptops break down, are dropped, or are stolen far more frequently than desktops.
What you want to do is to connect the external and use the OSX DVD to install a fresh system on the external. Then, boot from the external, install DiskWarrior and or DataRescue or other utilities, and see if you can recover data from the internal.
If you absolutely cannot get an external hard drive, then get a Firewire cable and borrow a recent model Mac from a friend. With the power off on both machines, Hook your Mac to to the other Mac using the FIrewire cable, boot your Mac into FW Target Disk Mode (Hold down the "T" key throughout startup) then boot the other Mac. If your Mac shows up on the other Mac as an external hard drive, proceed with data recovery / catalog repair from utilities installed on the other Mac.
Don't try reinstalling an OS on the MacBook until you have recovered data if you can. Installing stuff on a damaged drive just invites further damage.
Your MacBook is still under warranty, so don't rip it apart yet. Concentrate on recovering data, then let Apple replace the drive IF it is a physical problem. Apple will not recover data for you under warranty.
