I've encountered the following problem quite a few times, so I decided to write about it here on my blog so I can find the solution faster.
When trying to build various open source libraries, especially ones that were initially made for Linux and then ported to Windows, sometimes the following error is received:
Unable to find vcvarsall.bat
This comes up because it tries to build it using Visual Studio and it looks.... for an older version of VS (I think).
The solution is simple. If you have VS2010, execute: SET VS90COMNTOOLS=%VS100COMNTOOLS% at the command line and try again. If you have VS2012 run SET VS90COMNTOOLS=%VS110COMNTOOLS%.