Hi Lorena, you have several issues here, so let's take them one at a time.

I am designing a message and have a textbox that I want to set to have a
restricted number of characters. Normally it would hold 16, but for security
purposes, I want to show the last 10 of the 16. I stumbled onto PasswordChar
and thought that might help, but that hides all the information typed in. Is
there a way to set PasswordChar to hide only the first 6.

No. PasswordChar is an all-or-nothing setting. To do what you want to do, you'd have to develop a custom control and install it on every machine.

I tried validation
and was not sure how to set it so the number would have to be
999999999999999 and ,10000000000000000, if that is possible.

Is the field bound to the textbox a numeric field?

One error I
dont know if fixable but, I came across the problem right after the following
message "the data you entered is not valid" appears, and when I tried to
change the informtion in the box, the delete button and the backspace
wouldn't work.

Again, knowing what kind of data field you're using would be very helpful.
--
Sue Mosher, Outlook MVP
Author of Configuring Microsoft Outlook 2003
http://www.turtleflock.com/olconfig/index.htm
and Microsoft Outlook Programming - Jumpstart for
Administrators, Power Users, and Developers
http://www.outlookcode.com/jumpstart.aspx