Until you get to SQL 2012, you also have the "quick-and-dirty" version of that, using COMPUTE:

SELECT Curr_date, Action, AVG(Duration)/1000 as Avg_Duration

FROM Table_1

WHERE Curr_date = CAST(GETDATE() as DATE)

GROUP BY Curr_date, Action

-- added AVG just to show that multiple COMPUTE functions can be specified :-)

COMPUTE SUM(AVG(Duration)/1000), AVG(AVG(Duration)/1000)

It's sometimes easier just to slap on a COMPUTE than to rejigger the query ... and, as so often, in this case it avoids another full scan of the table (COMPUTE's a fun cheat, it died too young!).

Note that the COMPUTEd value(s) are a separate result set, and do not have any column heading other than the function used to create them, i.e., column is named "sum" or "avg" or "count" or whatever.