I might be the last person to know this but one of my favorite internal Microsoft tools is now external. Err.exe is a command-line tool that looks up error codes and spits out possible matches from various header files. This is invaluable when you're reading through a log and run across something like "Failed, err 0x80070003" -- just run err and you'll find out what this possibly means:
# for hex 0x80070003 / decimal -2147024893 :
# The specified path couldn't be found.
# 1 matches found for "0x80070003"
The download for err is available at http://www.microsoft.com/downloads/details.aspx?familyid=be596899-7bb8-4208-b7fc-09e02a13696c&displaylang=en. Download it and extract it to somewhere in %PATH% so that it's only a command prompt away.