From The Peopling of New York City
How to add a Shockwave Flash file (.swf) to the wiki
First, upload the .swf file
Then, go to the file list
Under the "name" column, find you file, and hold down CTRL and click "(file)" as it appears to the right of your file name, and select 'Copy Link Location'
Then, use the new SWF tag and paste in the location of the file you just uploaded, like this:
<swf width="400" height="400">http://macaulay.cuny.edu/seminars/lobel08/images/f/f8/Penguin.swf</swf>
Yes, you do have to specify width and height.
Here's the result:
Full documentation for how to use the Shockwave Flash tag is available here.