Steps to hide the drive

1. Go to Start > Run > type "diskpart".
2. Then type "list volume"
3. Now suppose you want to hide drive D then type "select volume 2"
Then a message will appear in same window { Volume 2 is the selected volume}
4. Now type "remove letter D"
Now a message will come { Diskpart Removed the Drive letter }
Diskpart will remove the letter D. In some cases it also ask for reboot. So you need to reboot in that case for this trick to work.
Now check your my computer, you will not find the D drive there. So its quite easy to hide you data with help of hiding the drive.
Windows XP is not having capability to identify the unknown volume. Your Data is now safe from unauthorized users.

Now if you want to access the Drive again. Repeat the first three steps as such and in the fourth step Instead of remove give "assign letter D".
It will give the unknown volume a name you will be able to access that drive again.