That is very strange. I have a whole bunch of Macromedia products, and none load at startup. But my guess is still that you must have some Macromedia utility or something that is set to load at startup and, failing to find it, redirects you to Macromedia's download page.
Check in your startup group (Start / All Programs / Startup) see if you have something from Macromedia there, or even any program with the default unknown icon. You can also type "msconfig" in the RUN dialog and look under the Startup tab, see if you have some Macromedia utility set to load at startup.