If you are wanting he starting and ending dates of the current week, try this:
To get Monday place this as the control source for a text box:
=DateAdd("d",(Weekday(Now())-2)*-1,Now())
To get friday use this:
=DateAdd("d",6-Weekday(Now()),Now())
Weekday (now) gives you a number (1-7) representing the current weekday. today(Wednesday) = 4.
Weekday(Now())-2 finds how many days past Monday we are.
6-Weekday(Now() finds how many days until Friday.
The only hitch is that by default, Sunday in the first day of the week. So if you ran the report on Saturday 7/15 it would give you Monday 7/10 and Friday 7/14, but if you ran it on Sunday 7/16, it would give you Monday 7/17 & Friday 7/21. If this is a problem you need to create a user-defined function so that you can adjust the firstdayofweek property as necessary. Then you can just use that function in your formulae. Let me know if you need any help with that. Hope this helps.
Eric