WinDiff is a graphical diff-like program published by Microsoft, and is distributed with certain versions of Microsoft Visual Studio and with the latest Service Pack. It is often criticized for its user interface, which doesn’t abide by system color settings or visual styles and is widely believed to be crude and unconfigurable. All settings, some of which would not have been out-of-place on a toolbar, have been placed in menus. Still, WinDiff is considered an improvement over the text-based diff-utilities like FC and diff that preceded it. (source, wikipedia)
WinMerge seems to be a valid alternative.