One way is to look at your paid search program and look at the members tab. Those that are marked acquired by the program are the new leads and the ones that are not are not marked acquired by the program, are your existing leads. But double check some activity records of your leads just to make sure.
I'm not sure I understand what you are proposing here. I have a dynamic list which tells me leads which have been created during a specific time span and it's based on the original source of the lead.
What field would I run that report on - to create a member list? We have multiple landing pages and sources for our programs.
How about this, I just looked at one of the smart lists that I created. My smart list contains the following:
Member of Program = true
Acquired by = false
Program = your paid search program ( you can add multiple programs)
success = true
Lead source = whatever your original source is.