Excel Formula: copy data and add "0000"

Hello,

how do I copy data from worksheet 1 into worksheet 2 (i know how to do this part), AND
1) delete the 4 digits at the end (i know how to do this part), AND (here's what I don't know....)
2) replace those 4 digits with 0000

ALSO
how do I
1) look up data from worksheet 1, and
2) find the matching data on a worksheet 2, then
3) copy data in a different column from worksheet 2 into a blank column on worksheet 1

THANK YOU VERY MUCH FOR YOUR HELP, I REALLY APPRECIATE IT! :)