you know, that is simple. i know it already from my occasional experience.

i managed to insert web links field in track properties window - but what i can't find is (i don't know how it is called...) the corresponding name for artist web links.
i mean (taken from default theme.dax):
albumlinks - is for album web links
artistlink - is for artist inside the database

but - i don't see anything like artistweblinks - for artist links outside the database, on the net!!!