Okay. I think I figured it out...
You have to access the index of the parent and make it a variable index. So, it would look something like this...
var nindex = this.parent.index;
var myDoc = event.target;
var f = myDoc.getField("MainBodySubform[0].ContractsReceived[0].ContractDetail[" + nindex + "].Name[0]");
f.doNotScroll = true;
This will change the index value as the form expands and keep the Do Not Scroll working...
If you have a nested subform it would look like this...
var nnindex = this.parent.parent.index;
var nindex = this.parent.index;
var myDoc = event.target;
var f = myDoc.getField("MainBodySubform[0].Sub1[0].Sub2[" + nnindex + "].Info[" + nindex + "].Name[0]");
f.doNotScroll = true;
Of course, I hear in Version 8 this will be in the UI so hopefully none of this will be needed....