Which IoC container is the easiest to get started with. This probably equates to which ones have the friendliest documentation. Not too worried about number of features.
R – Choosing a .Net Inversion of Control container for first attempt at Dependency Injection
Take a look at this DotNetRocks episode with James Kovacs: http://www.dotnetrocks.com/default.aspx?showNum=362
And this DNRTV where he rolls his own IoC: http://www.dnrtv.com/default.aspx?showID=126