Set up a new User, move all the relevant data files (documents, email
etc) and then delete the old user.

khtom21gs0dpn3bthjtlasmu7mmun80lss@4ax.com,

As has already been pointed out, the best approach to take is
to create a new user account. Keep in mind that you have to
logon to that new account at least once before you can copy
files and folders from the old account into the new account.

Either of these procedures will allow you to copy the files
from the old user account into a new user account.

How do I copy a user profile in Windows XP?
http://www.petri.co.il/copy_user_profiles_in_windows_xp.htm

To copy a user profile
http://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/s
ysdm_userprofile_copy.mspx?mfr=true

How to copy data from a corrupted user profile to a new profile
http://support.microsoft.com/default.aspx/kb/811151

You will have to use a third account which is a computer
administrator in order to copy the files. You can use the
built-in Administrator account or, if you're running XP Home,
create a temporary admin account that can be deleted once the
procedure is completed.

Good luck

Nepatsfan

Thank you for your answers, I will try to sort it out on my next
visit.

    The user profile folders (C:\Documents and Settings\Username)
_cannot_ be renamed, even if the associated user account has been.  So,
your best course of action would be to log on using the built-in
Administrator account, create a new user account, with the username
desired.  You can then delete the old user account(s).

HOW TO Create and Configure User Accounts in Windows XP
http://support.microsoft.com/default.aspx?scid=kb;en-us;279783

How to Copy User Data to a New User Profile
http://support.microsoft.com/default.aspx?scid=kb;en-us;811151