If possible download the DEB package from Quantal/12.10 and try to install that with Ubuntu Software Center. If there are no problems it will install. It looks like most installations are source based for network manager though.
You can get the source files and install that. There will be a 'how to install' or readme among the files. This does require more than average knowledge; you might need to tinker with settings or be able to understand errors or notices you get along the way. It is not for the faint hearted.
Unless you need to stick with 12.04 (it being a LTS) consider updating to 12.10. It is something that will be less hassle then installing from source.
When installing from source you can also try IRC channel #nm at irc.freenode.net. It might even be worth to see if someone can help you get the version from 12.04 fixed.