Although there are many ways to hide your drive and to prevent access to your drives. Either by setting regedit value for NoDrives and  NoViewOnDrive  or by using some system settings.

But I found one built-in tool “DISKPART”.

1. Go to Start > run > type "diskpart". A DOS window will appear with following description. DISKPART>

2. Then type "list volume" The result will look like: 

3. Suppose u want to hide drive E then type "select volume 3" Then a message will appear in same windows { Volume 3 is the selected volume}

4. Now type "remove letter E" Now a message will come { Diskpart Removed the Drive letter }
Sometime it requires the reboot the computer  or logoff and login will work. Diskpart will remove the letter. Now try to open that date even using at address bar. It will not open. Windows XP is not having capability to identify the unknown volume. Your Data is safe now from all unauthorized users. Don’t worry it will not tamper any of your data.

To access the content of hidden Drive repeat the process mentioned above. But in 4th step replace “remove" to "assign" i.e. type "assign letter E" . Note: It will not work for drive which is having system files, boot files etc like C drive in most cases. And it works in Vista , XP too. Didn’t test in win 7 but I think it will work there also.