Disabling programs for other users

Hi.
Can anyone tell me if there is a way of limiting the access to some
programs on one user account?

Let me explain why.....
I have 2 children who both have their own log-in, as well as myself and
my partner, which is fine.
The problem is that when they use the PC they both log-in to messenger,
again this is usually ok, except when they need to concentrate on their
homework.
So we have set up a specific log-in for homework, but we can't find a
way of disabling some of the programs (for instance - and especially -
Messenger) on THAT account.
I have been through the limited 'Homework' account trying to remove
some programs, to find they have been completely removed for all users,
and therefore have had to re-instate them.

Hope someone can help.
Phill.


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pipk62