You said you work with Bytemark; would I be able to host NZB files on the Bytemark servers? http://www.newsgroupdownloaders.com/nzbfile.html The NZB file is just an XML file, but it may reference locations on Usenet where copyrighted material may be.
PS: I'm not including 'source' code because what I had to do in vBulletin to make it work will have zero relevance to doing it on Vanilla (and most of it is full of vB's arcane "template conditionals")
Just create a conditional that says "if they don't have an avatar here..." that does this:
http://en.gravatar.com/site/implement/php (and make a nice default avatar for the newbs) :)