This code will give you the previous Monday's date..
=IIf(DatePart("w",Date(),2,2)="1",DateAdd("w",-0,Date()),IIf(DatePart("w",Date(),2,2)="2",DateAdd("w",-1,Date()),IIf(DatePart("w",Date(),2,2)="3",DateAdd("w",-2,Date()),IIf(DatePart("w",Date(),2,2)="4",DateAdd("w",-3,Date()),IIf(DatePart("w",Date(),2,2)="5",DateAdd("w",-4,Date()),IIf(DatePart("w",Date(),2,2)="6",DateAdd("w",-5,Date()),IIf(DatePart("w",Date(),2,2)="7",DateAdd("w",-6,Date()))))))))
Sean