If you are running Windows (2000 and later) you can do like I do and have the built in utilities in Windows do it for you according to a schedule.
AT = Microsoft's Scheduler Program
CIPHER = Microsoft's NTFS Encryption Program
Both applications are installed by default and can run seamlessly in the background. Cipher takes all available disk space on the drive/partition specified and writes zeros and random data to it making it unrecoverable by basic software-based recovery methods.
For example, if you want to wipe your C:\ partition at 8:00 PM every weekday, you would enter the following command at a command prompt:
C:\>at 20:00 /every:M,T,W,Th,F cipher /w:C
Then, at the command prompt, issue the at command without any parameters to verrify the schedule. It should look something like this:
C:\>atStatus ID Day Time Command Line------------------------------------------------------------------------------- 1 Each M T W Th F 8:00 PM cipher /w:CC:\>
Of course, you can always issue the cipher command when ever you like, such as after deleting a really sensitive document. Just keep in mind that it does tie up considerable system resources and depending on the ammount of free space, can take a long time to complete.
Hope this helps.