Ultimate Blog Marketing

I would like to know how did Google Adsense started, basically two questions:
They had where to put their Ads (websites) but they didn´t have Ads to display?
They had Ads to display but in what websites?

I am a resident of India .I have a blog on which i would like to post google ads.Should i pay tax on that in US and file return for that in US.Should i get a tax id for that .Please clarify.I have no other activities other than this connected with US.

Do any other companies, such as Yahoo or MSN, offer any affiliate programs similar to Google’s AdSense or AdWords? If so, which companies are they and what do they offer?

I am planning to earn some amount by google ad sense. so i want to start message board. Please help me by giving info regarding free software for message board, free hosting having option to post my own ads.

I wish to deploy a service similar to Google’s AdSense on my blogs (links to my blogs can be found in my profile on Yahoo! Answers). I wish to know whether Yahoo! Publisher Network is an offering equivalent to Google AdSense? If it’s different, then what is it and in what ways is it different from AdSense?