HI,
To find out how many referrals for PPC campaigns you are getting, you need to setup the campaigns to be tracked inside Analytics. If you go to the control panels for the profile in question, select manage campaigns, and then click on "Paid Search Campaigns", you should be able to import your Yahoo and Google campaigns. There is a seperate section in "Manage Campaigns" for importing your AdCenter campaigns. Once you have set this up, you'll be able to see how many referals you are getting from your different PPC campaigns.
With out setting those up, you would only see the referals by search engine, as Analytics will not differentiate PPC inbound clicks from any other inbound click from a search engine.
Brian
Brian Decker - MSFT