iWorkWeek=DatePart("ww",Now,vbSunday,vbFirstFullWeek) 
Select Case iWorkWeek
    Case 4
        WScript.Echo "Running week 4 maintenance"
    Case 12
        WScript.Echo "Running week 12 maintenance"
    Case 24
        WScript.Echo "Running week 24 maintenance"
    Case 48
        WScript.Echo "Running week 48 maintenance"
End Select