See the sample for Outlook 2007 here:
Flag an Email for Follow-up - VBOffice
See also the sample for how to call the function. Easiest is to have seven such functions. On systems where monday is the first day of the week, this one is for next tuesday:
Public Sub NextTuesday()
MarkItemAsTask 2-weekday(date,vbUseSystemDayOfWeek)
End Sub
This one for next wednesday (note the changing first figure)
Public Sub NextWednsesday()
MarkItemAsTask 3-weekday(date,vbUseSystemDayOfWeek)
End Sub
You can complete it yourself. For sunday the figure is 7. And this one is for next monday:
Public Sub NextWednsesday()
MarkItemAsTask 8-weekday(date,vbUseSystemDayOfWeek)
End Sub