You know what the day number of the week today is, by using the DayOfWeek function. (Sunday is Day 1.) So you can add or subtract the number of days from today to work back or forward through the week.
For example, Monday's date will be (assumes that the week starts on Sunday):
MondayDate = Get ( CurrentDate ) + ( 2 - DayOfWeek ( Get ( CurrentDate ) ) )
TuesdayDate = Monday + 1 (obviously)
Note that this will update every time you open the file or change record. Might be better to set it once by a script, and let the date fields be indexed.
If all you want to do is filter by 'Monday', Tuesday', etc (as opposed to the 1/2/2011, 2/2/2011), then why not just filter by the DayName?