Search Networks for Google examples include AOL.com, Ask.com, CNN. your ads will appear in search result pages on those networks.

Partner/Publisher Network examples for Yahoo! include iVilliage, USA Today, NBC your ads will appear in search result pages on those networks.

The advantages of having your PPC ads appear in the partner networks is the immediate increase in reach for your ads.

Content partners usually offer contextual ads. Your ads appear on a page with a story or content, not search results.  In this setting the search engine determines if the content of the page is relevant to your ad and keywords.  The user is not necessarily in “shop mode” when viewing contextual ads.

The worst example of this type of advertising gone wrong was where an advertisement for a fast food chain appeared on the same page as an article about an e.coli meat recall. When shown to a room full of internet users for 30 seconds they all thought the meat recall had something to do with the fast food chain. This is where negative words in your ppc campaigns can save you a lot of PR headaches. 

 Contextual/Content partner ads and Search Network Partner ads should be turned off  when starting a new campaign. Until you have a defined set of keywords producing a positive return on investment for your ppc campaign keep your testing limited to the search engine page results.

When you are ready to expand your ads, set up separate campaigns.