This AppleScript sets the titles of photos imported into an iPhoto library based on a set of text files in a given directory:
tell application "iPhoto"
set bound to count of (photos in current album)
repeat with i from 1 to bound
set oldname to (name of photo i of current album) as string
set mytitle to do shell script "cat /Users/user/Desktop/Import/" & oldname & ".txt"
set the title of photo i of current album to mytitle