windows 7/64
we followed the instructions here
http://wpilib.screenstepslive.com/s/4485/m/13810, then, after using the wizard to set up a test project, the code would not compile saying, among other things, WPILib.h not found.
the problem turned out to be the env var HOME was set to something other than whatever the default might be (because we sometimes use gvim which keeps its init files under $HOME). I found the installed WPILib.h by searching the entire c: drive; on my system it's under c:/Users/User/wpilib. in eclipse under window>preferences>c/c++>build>build variables you will find WPILIB is set to $HOME/wpilib. if you change WPILIB to c:/users/user/wpilib and reindex all works fine. I did not try instead moving the wpilib/* tree under $HOME because I was afraid it would mess up automatic updating.
I believe this happens because the installer uses $HOMEPATH as the location to install wpilib, but eclipse is set up to use $HOME to find it and these values may not be the same. I did quite a bit of wading around on the net without finding clear supporting evidence, all I know is the above fix worked for me.
<edit> it would be better if the installer put wpilib somewhere specified at install time with a default like c:\wpilib or similar (similar to the way c:\frc works). the HOME/HOMEPATH issue will be a problem on any machine where more than one login exists.