Diffrentiating tracking from different Search Engines

[seema345]

My technical team says we cannot diffrentiate leads from different search engines for one website. They give me stats which shows all conversions from all searchengines. I believe there has to be a way to diffrentiate different leads from different search engines. Can someone guide me to as to what to suggest to them?
The reason I am posting this in the Yahoo Paid Inclusion category is that we are in the process of siging up for Yahoo PI and need to seperate leads from Yahoo from that of other SE's.
Thanks

[webmaster]

Why can't your technical team check the user agent's referrer header when the user enters your site, attach it to the session in some fashion, and log it upon conversion?

Maybe I'm not understanding the question.