Thanks for the fast reply, worked a treat. In fact I didn't have to change the size of my new icon (48 x 48) to match the others (60 x 60) as it seemed to scale ok.
One other question: my name appears next to the icon twice, with andy positioned directly below Andy, whereas root only has one name, no capital letter. It was like this before I changed the icon. Any ideas why my name appears twice?