Assuming that you're not using the dynamic parameters that are available in CR XI, the following is the usual means:
Add in the default value maually and hit the arrow key to move it over. I tend to do this first, otherwise you'll have to use the up arrow to move it to the top of the f it's already populated, remove them all and then add in the dept1, then add them all again.
Type in a description for dept1 of something like "Please select this for all values", and make sure that the values and description are enabled for parameters.
Now in the Report->Selection Formula->Record place something like the following:
(
if {?MyParameter} <> "Dept1" then
{table.field} = {?MyParameter}
else
if {?MyParameter} = "Dept1" then
true
)
Note the else if fully defined and the paranethesis are there to help ensure sql pass through.
-k