Displaying multiple files

[Jason Snyder]

I have the following wind data files that cover the following time ranges:

uwnd.2001.nc  January 1 2001 to December 31 2001
uwnd.2002.nc  January 1 2002 to December 31 2002
uwnd.2003.nc  January 1 2003 to December 31 2003
uwnd.2004.nc  January 1 2004 to December 31 2004

I want to create a variable that would display the average wind from
January 1 2001 to December 31 2004.  How would I go about doing this?  Can
someone show me a method for opening all these netcdf files at once and
creating an avrerage wind in the above time period specified from these 4
files?