how to add image icon to primary or secondary links?how to get logged user name?

question:

1. how to add image icon to primary or secondary links?
for example: I want use a shopping cart icon with text "your cart" as a secondary link, how can I add the cart icon on to it. it seems only accept text as links.

2. when a user logged in, where or how can I get the user name for further use? in a variable or stored in database, either way, how can get it and used in the preprogrammed files?

thanks a lot

george