death's "Saddam Crackme"

[difficulty: 5][protection: des, scrambled function table]

After being des-decrypted (key derived from GetVolumeInformation()), your serial is used to unscramble an array of function pointers which are critical to the protected application (a cool desktop switcher prog called Smirk).

To solve it, you can make a a small number of guesses (relative to the entire size of the table) at proper locations of function pointers within the table, and then search which serials yield arrangements that fit your guess.