Yes it is. However, if you're not running ntfs you'll need to convert to it to achieve what you're after. Once you're running ntfs, open windows explorer> Tools> Folder Options> 'view' tab> scroll to the bottom of the list and untick 'use simple file sharing.' After that, right click on the folder you want to restrict access too> properties> 'security' tab - set your user restrictions there. And of course, set up quest accounts and password protect your own account from casual use by others.
If you've restricted access to other user accounts... those accounts are denied access completely to the folder - clicking on it causes a dialog box to come up saying 'go away.' In affect, your user account password is the folders password.
I think you're asking if you can password protect a folder even in your own account... I don't think you can without some kind of third party support such as archiving the folder and setting a password on it. Problem with that is you can still view the contents of the file, you just can't extract/access anything in it w/o the password (unlike user restrictions where you're not even allowed to view the contents). There are other compression utilities available, like 'Camoflage,' that will 'hide' one file inside of another one and require a password to extract it/them.
Another option would be to create a 'secure' partition that would normally be restricted to all accounts expect a specific one, requiring you to log-off of your normal account into the secure one to access the protected folder(s).
While you're looking for a solution, be careful about encrypting things. If you have a computer crash and haven't taken the appropriate measures to unencrpt your files under a new installation... those files are pretty much toast, encryption is a VERY tough nut to crack.