This link
http://lesswrong.com/r/all/recentposts
gives a page which lists all the recent posts in both the Main and Discussion sections. I've posted it in the comments section before, but I decided to put it in a discussion post because it's a really handy way of accessing the site. I found it by guessing the URL.
You can use this Python script I wrote. (Tested on Python 2.7.) It outputs to a CSV which can be imported into Excel, OpenOffice, etc. and put into a xls if you really want. Read the code comments to see where you have to paste in the recent post text and where you have to set the output filename.
Thank you. But I'd rather have the original file, from which the (sub)pages have been generated. The reverse engineering is the second best way.