Ok, it’s not what I would call a Wiki (at least in Sharepoint version 2007). But if you have to use with Sharepoint and there is no way to maintain a separate, real Wiki you have to use Sharepoint’s Wiki.

In my case there was the task to migrate existing content from a JSPWiki to Sharepoint’s Wiki. Sharepoint Designer cannot be used for adding contant (http://social.msdn.microsoft.com/Forums/en-US/sharepointcustomization/thread/451f355f-0c4a-44bd-8071-112eea6e5b2b; at the bottom of the page). Therefore I used Sharepoint’s WebServices. A pretty good example can be found here: http://sites.google.com/site/sharepointwikiuploader/.

You can use a simple web crawler to get the content from the old Wiki if you don’t have access to the file system, DB or whatever.