How to approach code review with limited resources [on hold]

I've been given the following task:

A company is giving source code for its product (comprising over 1 million lines of C++, Java, with some assembly) for my review. The code will be loaded onto a Windows machine that I do not control, has no USB ports, no network, and is a small controlled room. I must somehow sift through the code, figure out where the implementation of Action X is, and then trace through the code to see how Action X ties into the rest of the product.

The last time I did this, they gave me the code along with Notepad. Since I couldn't add software, that was it. I found myself using DOS command shells to get a grep-like ability with FINDSTR /R but this was painful, as you might imagine.

My question: how might one approach this chore in a logical and efficient manner? If you were given this task, how would you approach it?