I have been asked what utility is good to use in the Windows environment that performs a similar function as the Unix command "diff", i.e., compare files line by line. My answer is: WinMerge.
WinMerge http://winmerge.sourceforge.net/ is an excellent tool that provides "visual text file differencing and merging tool for Win32 platforms. It is highly useful for determing what has changed between project versions, and then merging changes between versions."
I highly recommend it.