All the IIMs take students thru the overseas application- for NRIs and foreign nationals. The details for applying are given on each of their websites, the eligibility criteria varies a bit. For NRI, u should be stayin outside India for a period of atleast 18 months - either studyin/working.
But u must have a very good GMAT Score..atleast a 90 percentile, also very good academic background and good workex if possible. They take very few students each IIM makes an offer of 3 students (average) roughly. They get around 50 - 100 applications...Ahm, Indore n Koz conduct interviews if shortlisted. The competition is quite high n u shud make an honest assesment of yourself before applying. Good essays and answers to questns r required by some of the IIMs and also recommendation letters ( 2 to 3).