MSM422 and One Laptop

[Edgeborough]

I have 19 MSM422 AP around the school and in one area I had 3 Laptops connecting to on MSM422 and working well, But recently one of the Laptops (running XP) has decided to connect to a different further away MSM422 and will not connect to the nearest one. I have tried to disassociate the Laptop but nothing happens. Any ideas out there please 

[JesseR]

Which AP a client connects to is really determined by the client itself and its drivers/software.  Only way I can think of to try to persuade it to connect to the closer AP is the reduce power on the other one.  Also this can happen too if co channel interference is poor on the nearby AP.