Get a linux recovery or live-cd and boot your pc from it. make sure it does not write anything to your disk!
Now you can start recovering.
I recommend mondo or scrounge-ntfs for ntfs. They are built-in into most live-cd's.
If everything fails there is still hope:
there is a specific structure inside the wallet.dat-file, for example it contains lots of "blockindex"-strings, your public addresses (you can still get them, for example from your pool, do you?) and some more.
i wrote a little tool that searches your whole harddisk for this structure and recovers all private keys it finds - even if there is no reference to the file in the file system, even if the file is partially overwritten - and generates a new wallet.dat file from it.
Pulling private keys directly off the hard disk is fast enough that it might even be worth making it the *first* recovery method you try, unless there's other information in the wallet or elsewhere that you need to recover. Unless you've got a slow PC or a very fast disk, my (publicly available, linked to upthread) tool for doing it can scan your drive as quickly as it can read data from it. It does really need optimising a bit more though.