GitHub is NOT a version control -- it "hosts" the version control system called "Git". Aside from the pun, this is a very important difference -- know it well.
Regarding enterprise use, I can tell you that git is as smart (and convenient, and better) as something like SVN. And, you can choose a suitable version control strategy (workflow) based on the size and scope of the project (and your team). Non-distributed systems can't afford you this flexibility.
For Windows, check out Msysgit or Visual Studio Extensions for Git -- git works very well on Windows. Also, windows users look at this training series from TekPub -- it is all Windows.
UPDATE [Feb 2013] getting started with git in visual studiogetting started with git in visual studio
Your question is not uncommon, and you could google about it and get a lot of text explaining you why and how (and whether) to use git in the enterprise.
- Go read this, this, and this
- Look at GitLab, a self-hosted application that provides an interface similar to GitHub
- Look at gitolite project
- Look at Git Hosting options:
Still don't like Git? Look at another DVCS called Mercurial.
