One possible merge tool for windows is kdiff3 which works great.
after installing kdiff3 git needs to be set up.
This blog post describes it (http://www.blog.project13.pl/index.php/coding/1192/setup-git-on-windows-to-use-kdiff3-as-its-mergetool/) but its repeated here:
add the following to .gitconfig
[merge]
tool=kdiff3
[mergetool “kdiff3”]
path = C:/Program Files/KDiff3/kdiff3.exe
keepBackup = false
trustExitCode = false
Tags: .gitconfig, git mergetool, kdiff3