XP Security

[Allan P. Collins III]

I was trying to secure the "C" drive on a user's XP
machine & am now stuck & unable to logon. I was logged
onto my domain with an account that has administrative
access. I went to "My Computer" selected the "C" drive,
then "Properties" & hit the security tab.
By default "Everyone" was selected. I added my admin
account, the domain administrator, & the user of the
workstation & gave them "Full Control," then
removed "Everyone," & hit apply. When I try to log back on
to this machine, I am getting errors as follows:
When trying to logon to my domain after typing my
username & pw, A window will pop up with a red button that
has a white "X" inside of it & an O.K. button below. Click
O.K. & you are taken back to the ctrl + alt + del logon
screen. If I try to logon locally as the machine admin, I
receive an error window stating the following:

User Environment:
Windows cannot create a temporary profile directory but
has logged you on with the default profile. This may be
caused by insufficient security rights.
Detail - Cannot create a file when that file already
exists.

I can map & access drives on this machine, I just can't
logon. Will I have to reinstall XP to correct this?

Thank you,
Allan P. Collins III