"This report, by its very length, defends itself against the risk of being read." (Winston Churchill)
The problem with policies and procedures is summed up by the Winston Churchill quote above.
I think an intranet/wiki is a good place to start but there are a few gotchas. It is quite a skill to be able to do the following:-
1. Write something that is both useful and easily digestible
2. Structure information so it is easy to navigate
3. Categorise information so others find it is easy to find
When I write wiki entries I take the following approach
1. Start with a basic page that summarises the key points
2. Always include a "last updated date" and "last updated author" at the head of the document below the title
3. Always include a table-of-contents (preferably hyperlinked to the subject headers) and "quick links" before the first subheading
4. Always give a concise description of what the document is for so the reader can determine if it is going to contain something useful
5. Hyperlink to documents giving more detailed information about the key subjects.
6. On a child page always have a link back to the parent in the "quick links" if you don't have a bread crumb trail.