If you upgraded to TFS2008 then you could use a Sharepoint Services 3.0 portal which includes a basic Wiki feature. There are many other reasons to upgrade to TFS2008 (less bugs, better speed, more features, great back-compat with VS2005 etc) but just thought I'd mention it.
Here's an interesting way one project manages community updates to their wiki, while still keeping tight control, as for source code:
My proposed workflow is this:
Manually create a fork of the Taffy wiki on your Github account:
Create a new repository on your github account. Let's call it "Taffy-Wiki".
Clone the Taffy wiki repo to your local machine somewhere: git clone git@github.com:atuttle/Taffy.wiki.git
Remove the original "origin" remote and add your github repo as new "origin" git remote rm origin and git remote add origin git@github.com:<YOUR_USERNAME>/Taffy-Wiki.git
Make your proposed changes locally, then push them to your github account: git push -u origin master ('-u origin master' only required the first time; afterwards just do git push)
Submit a ticket to the official Taffy issue tracker requesting me to review your changes and merge them in. Please be sure to include a link to your repo and describe what you've changed.
If it were me, I'd create an issue in the main repository (that is, the one you forked) suggesting an update to the wiki. If issues aren't enabled, then email's about the only other option I can think of.
Best Answer
On TFS 2008 from the web interface:
1) click "Site Actions"
2) select "Create"
3) fill in the fields, select "Collaboration | Wiki Site" as the template
4) click "Create"
Should be the same steps for TFS 2005 and workgroup editions of both.