Thanks for trying the rei viewer.
1. Git
We have found that Cygwin's git isn't reliable on Windows, so we
recommend Msysgit instead. There is no problem in installing both,
since Cygwin's git is only available from the Cygwin terminal, and
Msysgit from Windows command prompts . So, just open a command prompt
and issue the git commands from there.
2. Login
The fields on the login screen are:
a. Login URI without the http prefix (for example: osgrid.org:8002)
b. first name
c. surname
d. password
3. Graphics card
This is simply a warning that appears when you are using a card that
hasn't been tested yet. Let us know if there are problems
(http://github.com/3di/3di-viewer-rei/issues)
Hope this helps,
Johan Berntsson