Richard....the Outlook express thing is easy to solve.....
Open the program up from the START menu, then click tools, accounts, and select the properties for the account there......
You'll find that there is a box for enering the return address that will have this other chap's address in it, ....change this to your address and Robert's your father's brother.
If there is more than one account, you can either delete the others (assuming it's only you who uses that machine) or change them.
Set your own account as the one to be used by default, then try a test email sent to yourself to make sure it works.