1) that's an absolute URL

(relative means relative to the current directory, so e.g. something like
../dir1/file.ext), and yes, that should work. For SWFs you might want to have a look at the parameters
img@sameappdomain,
img@samesecdomain (second one not yet documented, but same as the first one just for the SecurityDomain) and possibly
book@allowcrossdomaindata.
2) you'll have to parse that feed first, MegaZine3 can only handle images. Feel invited to write a Flickr plugin, though
