This is a conversion method that I discovered by accident and have found very useful. With the more extensive use of flash files on the web over the past few years, I have come across many flash files that are sent out as .exe files that are only playable on PCs.
But, I discovered from comapring them in a Hex editor to .swf cross-platform files, there is just a header thrown onto the start.
If you open a .exe flash file in Hexedit, search for fws (notice it's swf backwords). If you find it, delete all the chars exactly before it and save the file as .swf. It will play in Quicktime or a browser now.
If you don't find fws, sometimes the flash files are compressed. The only type I have come across are Rar files. In that case search for rar! and delete the header and save as .rar. Now uncompress in stuffit and search for fws again.
This works for a great number of flash files but I don't think it works for all of them. I have found very few that don't though.