Use something similar to something else you use (Score 1)

The most important thing about any documentation solution is that people use it, otherwise it is useless. To minimize the costs of using it, I suggest you find a solution that is similar to something people at your organization are used to using.

I had the same problem land on my desk a month ago. All of our policies and procedures were stored in a big notebook that was horribly out of date and that no one read. Since we use Trac for our dev department, people were used to the wiki formatting on it. I installed MoinMoin as a corporate wiki, which uses the same format.

MoinMoin is great because it uses basic authentication from apache, so you can authenticate it against whatever you have (like Active Directory), and people don't need another set of passowrds. It is simple to use and also easy to backup. Also, if you have a corporate intranet already, it is not difficult to integrate.

The wiki is great because anyone can modify it without alot of fanfare. However, if you choose a solution that is yet another thing to learn how to use, no one will take the time to use it. Again, the most important thing in my opinion is to lower the cost to the end user so that it is easier to post the information on the wiki than answer the same question again and again.