I've tried to explain that it is not about buying a server, it is not about installing a blog engine, it is not about controlling access.
Blogging is a tool but it is not about tools. Blogging is having a culture of sharing, and employees are not going to start sharing just because they have blogs (the ones that like sharing are very probably doing it already, either with blogs or something else). Blogging is about creating a culture where people do not fear to say what they think. Blogging is not about «build it and they will come». People need to understand what it is not working that blogging can help.
So why do you want blogging for? How do you see blogging in your organization's communication strategy (improve internal communication, integrate it with your KM efforts, foster good will in your environment, expand your networks, attract talent, all of them, other)?
Cause you know, to choose a blogging tool, you need to understand the organization so you can choose it according to the needs of the people that are going to use it.
If blogging for you starts and ends with a tool, maybe it's best you do the obvious: do nothing.