Retrieve data, add new fields and enter it in new table

Hi, I am trying to do the following: - retrieve data from a table based on the $id field (easy enough) - add a few more fields to the data set, then - enter the data (and new fields) into a new table (based on the selected $id field) I'm just not sure how to structure this, do I use a temporary table, add the new fields, then move the data set into the target table? Or is there a better way? Thanks Justin