I am presenting Git to a 10 man programming team who currently use Visual Source Safe.
They need to host their Git server inside the company. Windows or Linux. Direc
There are lots of git management GUIs out there if you want to run it yourself. gitorious is nice, for example.
For your authentication needs, that's mostly up to you. You may have a hard time having ssh honor your preferred auth technique (last time I did anything like that, I modified ssh to read keys out of LDAP).
The web interface could do whatever you'd like, I'm sure. I'd probably just leave it open on the inside of the network, though.