Are you sure git is in your path?
I did (I have Chocolatey installed):
> cinst nodejs > cinst git
(You might need to restart your shell here to get the correct environment variables.)
> npm install -g ungit
Make sure you put -g for 'global' on the npm install line.
That should give you a working copy.
Note that if you have password protected upstreams (e.g. GitHub) then you're going to want to do this (or ungit will cause git to ask you for your credentials on the command line and it won't really work since it asks twice):
ID:295
Name: ungit
Street:: 123 main street
Street::
City :: tools
State :: language-javascript
Country :: technology-developer-www
Postal :: n/a
STATUS: Go
PRIORITY: 0
OWNER ID: 75
DESCRIPTION: web based ui for git,