Way #1)
(a) Go into Control Panel / User Accounts and set up multiple user profiles on the computer. Change the "Account Type" for own profile to "Computer administrator."
(See Note #2 below)
Set the built-in password protection feature for your own user profile.
Change the "Account Type" for all other user profiles to "Limited."
(b) Log out of your user profile and log into the Administrator user profile (log off your profile, then press Control-Alt-Delete keys all together twice). Set the password for it too.
(c) Start / My Computer / Right click on a drive that you want to hide, select Properties / Security
(In case you don't see a Securities tab, then you have to turn off "simple file shaing", after which you should then see the Security tab)
(d) Clear checkboxes to remove read/write rights to the hidden drive for all other user profiles. Others will still see the drive letter, but they won't be able to open it. Other users will not be able to undo this access restriction because of their Limited profiles. Even a knowledgable user who tries to circumvent by loggin into the Administrator profile will be blocked by its password protection.
Way #2)
Install free Microsoft Tweak UI. Put it's icon on the Start / All Programs menu of your user profile ONLY. In Tweak UI, click My Computer / Drives and uncheck the drive you want to hide. Any other user profiles then will not even see the hidden drive letter at all. Neither will you. Any time you want to acces the hidden drive it only takes a couple of seconds to reverse this.
My main computer has 4 user profiles, and I do both #1 and #2 above. Anytime I want to access the hidden drives (I have 3 hidden drives) it only takes maybe 10 seconds to make them visible using Tweak UI.
#3) Password a drive: Sorry, I don't know how to do that.
Note
On your storage drive, suggest you make a folder into which you back up your entire main driive, or at least My Docs
Note 2
In another thread,
spike spiegal said it's safer to
avoid surfing with admin rights
(so malicious stuff won't have rights to install itself. Good point.)
If you want max safety set the "Account Type" for your own profile to "Limited" too. That'd require you to log into the Administrator user profile every time you wanted to access the hidden drive. Personally I'm usually too hurried for that, but as
spike spiegal said, it would protect you even better.
other thread