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Daves right, if all you do is delete the stuff you no longer need and keep the applications he needs, it's likely they will inherit problems you had or where about to have.
A nice clean install with fresh installtions of all the application with their default settings is always nice. The performance is better, it runs smooth and they won't come to you complaining over bad performance etc.
Of course there is way more to it then that, but I'm sure you get the general Idea.
A full format and install of WinXp will take no mor ethen an hour. Hit the windows update site and get it up to spec. Install the drivers and applications they want and your good to go. Thats how I would want something if it were sold to me, saves on hassle and allows them instant access to everything they need with little to no aggrivation.
*to lazy to spell check*