You are actually half right half wrong, it is said that your have to delete and write over something 32 times to have it completely untraceable from a hard drive. So you and your little delete *.* /y aren't going to do much, I can still see what you had on your drive. If I really wanted to be an *******, I could use this little device that costs 300 bucks, and copy the entire data from one to another drive. At blazing speed, and have your drive back in your hard drive before you got back from lunch.
And even then, the data might still be recoverable. The best thing to do would be to build a program that iterates through every cluster on the disk, writing random data.