Bernhar when I read Your first post more carefully I realise that You want to know the first day of the week of some date not the number of the day of the week:
Try this (not tested):
FUNCTION FirstDay(dDate)
LOCAL ret_val
IF DOW(dDate) == 1
ret_val = dDate - 6
ELSE
ret_val = dDate - DOW(dDate) + 2
ENDIF
RETURN CDOW(ret_val) + " "+ DTOC(ret_val)
Against Stupidity the Gods themselves Contend in Vain - Johann Christoph Friedrich von Schiller
The only thing normal about database guys is their tables.