Extension Manager only installs/manages extensions for the same version of products. Extension Manager CS5.5 only installs/manages extensions for CS5.5 products such as Dreamweaver CS5.5, Flash CS5.5, InDesign CS5.5, etc. If you want to install extensions for Flash CS3, you have to install Extension Manager 1.8, which you can get from http://www.adobe.com/exchange/em_download/em18_download.html. You also have to ensure "flash eff2" supports Flash CS3. I don't know what "flash eff2" is.