Limited users can view folders belonging to others

I have set up my xp pc with a number of 'limited' user accounts and one
administrator. All of the limited users can see the files and folders
belonging to two other accounts (when clicking on my computer) - and also
each these two can see each others files and folders (by clicking on my
computer). The other limited accounts only see their own and the two just
mentioned. The two 'problem' accounts have names with letters in the first
part of the alphabet - just a co-incidence? I changed the usernams to begin
with an 'R' - the accounts were no longer visible to others. Why is this
happening?
Thaanks in advance for any assistance.