This paper presents a user model: a computer program which examines the behaviour of a real computer user. The model encompasses four aspects of keyboard use which can present difficulties for people with motor disabilities. Where relevant keyboard configuration options exist, the model chooses appropriate settings for these options. The model bases its recommendations on observation of users typing free English text. It is intended to form part of a dynamic configuration support tool. Empirical evaluation showed the model to be very accurate in identification of a given user's difficulties. Where recommended configuration options were tried by the participants, high levels of error reduction and user satisfaction were found.