Howto use grep command

Hi all ,
i am having a table which contains start date and end date
for ex ..
startdate enddate
12/03/2011 12/04/2012
11/03/2011 20/05/2011
11/04/2011 28/07/2011

how to grep startdate = 12/03/2011
enddate = 28/07/2011

i need output :-
startdate:12/03/2012
enddate:28/07/2011

Any body know the solutoins help me........

awk '$1 == "12/03/2011" || $2 == "28/07/2011" {print}' file

head -1 file | awk '{ print "startdate="$1 }' 
tail -1 file | awk '{ print "enddate="$NF }'

awk 'NR==1{print "startdate:",$1}END{print "enddate:",$2}' infile

Useless Use of Cat