Transfering e-mails to another PC

Dear Colleagues,
I am changing the computer of my boss who uses outlook express e-mail client. He has created loads of sub folders in outlook express and he wants this folder structure and all e-mails transfered to the new computer. Is there an easy way of doing this. Which files holds all the e-mails on the old PC? Was thinking of copying such a file over to the new PC to overwrite the existing and probably empty one in the new PC.
Please help help help.,