I've been meaning to do a write up on tools for applying patches on Windows but haven't had a chance. For now I'll just leave it at this list.

DiffUtils 2.8.7 - show differences between files
http://gnuwin32.sourceforge.net/packages/diffutils.htm

CoreUtils 5.3.0 - GNU file, shell and text utilities
http://gnuwin32.sourceforge.net/downlinks/coreutils.php

CygUtils 1.2.9 - miscellaneous utilities including dos2unix and unix2dos (which you'll need to convert the line endings to keep patch happy)
http://gnuwin32.sourceforge.net/packages/cygutils.htm

Patch 2.5.9 - apply a diff file to an original
http://gnuwin32.sourceforge.net/packages/patch.htm

Wget 1.10.1 - retrieve files from the WWW
http://gnuwin32.sourceforge.net/packages/wget.htm

WinMerge
http://winmerge.org/