A very nice, although fast-paced, introduction to git is http://gitcasts.com/posts/railsconf-git-talk
This is about git on Windows, from the same guy: http://gitcasts.com/posts/git-on-windows
Now, practical stuff. As long as everything is still in Subversion for us, using git's built-in Subversion bridging is cool. Just read this to get started: http://www.viget.com/extend/effectively-using-git-with-subversion/
I did that for PHPCR and TYPO3CR last week to be able to branch for some experimental stuff I'm doing, and that works beautifully. Creating a branch, committing to that branch, switching back to master, changing something there, committing that to Subversion. All worked well.
Most impressive is the speed with which all that happens (aside from the svn commit). Looking at the history? Diff? All lighting fast.
Granted for the Mac there is GitX, a nice frontend. But git comes with built-in GUI tools as well, git gui and gitk. TextMate has very complete Git bundle, and there is EGit for Eclipse (still rough). And TortoiseGit.
That might be helpful. I hope. :)