the current (politically?) popular theory in Indian history is that the Indus Valley Civilisation gave rise to the Indo-European language group

Only if you're Aryan linguistically, i.e., speaking an Indic IE language. The Dravidians (mainly Tamils in the stuff I've seen) have of course figured out that Harappa-Mohenjodaro civilisation spoke a Dravidian language. Also, the whole Aryan Invasion Theory is a bit of a strawman in that few linguists/archeologists these days hold to the classical hoardes of IE sweeping in from the Urheimat and conquering the autochthonous aborigines that Max Mueller et al imagined. I have some links on one of my blog entries:

http://www.bisso.com/ujg_archives/000223.html