I am looking for a way to backup a SharePoint 2007 wiki and view it offline, if possible without using the central administration and stsadm. Any suggestion?
There's no way to get wiki data out of Sharepoint - at least not without admin access to the server or database.
The best you can do is to create a new view with the columns Name and Wiki Content, then copy&paste from your browser into Word.... yes, I know it sucks but we haven't found a better way either, and the corporate Sharepoint team can't offer anything better either.
It sounds like you're already invested in Sharepoint, but in case you're just starting out, I'd like to suggest that you look at alternatives, too.
The wiki functionality was probably thrown into Sharepoint for marketing reasons, so MS can say that they offer a wiki. But the Sharepoint wiki offers very poor functionality.