Applications :: Using Pages For Physics Lab Report

I'm using Pages v1.0.2 to write my lab report, and am wondering if there is a way to do two things: How can I write an x sub i [x with a small i by the lower right side of the x]? How can I insert a summation notation symbol [∑] WITH the index information below and above it? Inserting the symbol itself is easy with the OS X Characters Palette, but putting the i=1 on the bottom and the N on the top is what I don't know how do in a good looking way. And since I'm probably going to run into more things like this in the future, is there a resource where I can look this stuff up?