cross forest migration, creation of source .csv file

id like to migrate users from one exchange to another.  seperate forests, same email domain.  (retire old in favor of new)

this page mentions using a .csv file as input for a migration batch process.  how do i go about creating the .csv of my source users?

http://technet.microsoft.com/en-us/library/jj219166(v=exchg.150).aspx

any tips?  thanks!
Jonathan