Excel: use if to find & change text in column

Hello,

i want to search column "a" with numbers as text as follows:

#305
#777
#78
#82
#884

i need a formula that will search column A and change any two digit numbers to three digit with a leading zero. i want the change to take place within the existing data in column a so that example data:

a1 lkjljlk blah #305
a2 dkfjalfj blah #55

would end up as

a1 lkjljlk blah #305
a2 dkfjalfj blah #055

thanks and thanks to everyone for all this great information on this site

vista
excel 2007
firefox