Your 'Avatar' is the tiny picture that appears next to each of your posts. The much bigger 'Profile picture' is only displays when someone views your profile by clicking your name.
Both of these are optional and you can change them yourself by clicking the word 'Profile' at the top of the page as Mike Gadd mentioned. There are loads of avatar pictures to choose from but, to be honest, they're mostly naff.
If you don't like any of the available avatars you can email a picture of your own to me at
sv_chatpage@symi.eu.com and I'll make it your avatar.
In the meantime, since you're always baking I've set your avatar to be a cake. Hope you don't mind.