thanks Dano!
I just found the answer on the board in thread
/t/4024/1
which is similar approach as you suggest, ie create a new Action
with properties
Action type: Format value
Field: BAND
Formatstring: %Artist%
and it works great! Saved my bacon - I wasn't looking forward to updated 10.000 tracks by hand in WMP, ugh!, that would have been a real nasty exersize.
thanks for the help!