It won't default to specific values if that's what you mean.
You can however set permanent default values and if the user doesn't change them it will default to the last week.
The record selection formula->record would then read:
//assuming a default value of 1/1/1970
(
if {Datestart} <> cdate(1970,1,1) then
{table.field} >= {?Startdate}
and
{table.field} <= {?Dateend}
else
if {Datestart} = cdate(1970,1,1) then
{table.field} >= currentdate-6
and
{table.field} <= currentdate)
)
-k