I recommend using Mediawiki to create your wiki.  It is the software that powers Wikipedia, so it is proven to be very reliable and scalable.  It is the most popular wiki in the world, so many people are already familiar with the syntax.

On the subject of syntax - the syntax for this site's comments is identical to Mediawiki syntax.

A popular way to implement a wiki is to use a subdomain.  For The Oil Drum, it would wiki.theoildrum.com.

The Joomla Content Management System has an extension that allows for Mediawiki integration into a Joomla site.  This configuration allows you to maintain your existing sidebars, headers, etc...  An example can be found here  I'm not sure what CMS you're using for this site, so I'm not sure if that is even an option.

I've ran three different wiki packages (TWiki, MediaWiki, and MoinMoin). I actually don't like MediaWiki because it really doesn't allow you to do much in terms of formatting. This is a feature that makes the site easier to manage, but it certainly restricts your freedom. For example, as far as I could tell, images can't function as links. That one was a killer for my application.

TWiki is more or less the opposite in terms of flexibility, but it is necessarily harder to manage and has had significant security issues. It works very well as the wiki software for a work group (with extensions for calenders and task lists (action items)).

MoinMoin is somewhere in between and allows the author to

If it were me, I'd just direct everybody to the appropriate Wikipedia pages and have at 'er. That would get more eyeballs for a lot less work.

I just noticed the Wiki Books project (www.wikibooks.org) which is also by the folk that bring us Wikipedia. It seems to me that a Peak Oil wiki book would be perfect Oil Drummer supported project.