What's a meme? Is it the same as a viral? Yes, kind of, but no, not really strictly speaking ...
A meme is something in the air, that goes around, passed on from person to person. Sounds pretty viral-like so far.
However, it's not the same as a viral which is generally content (e.g. video) that self-propagates as it's forwarded from person to person (via email, Facebook etc.). I suppose you could argue that virals are a little passive - I find a funny video, I have a laugh, I pass it on to some friends who have a laugh at it too and pass it on in turn ad infintum (or usually until it comes back to me).
A meme involves more participation in the creation of new - in the sense of remixed, remade, adapted - content.
Here's an example: someone comes up with the idea of expressing song lyrics in the form of a PowerPoint-style pie chart graphic. The chart goes up - on Facebook, Flickr etc. - and in a short space of time there are hundreds - if not thousands - of riffs on the theme. If I meme (I think it's used as a verb) I'm creating my own take on an established convention - in this case re-articulating the lyrics of a song as a user-friendly graphic. There's stylistic play and parody aplenty here as memers (I think it can be used as an agent noun) simultaneously spoof pop lyrics and business-pitch presentation styles.
Where's it come from? Dunno ... but it looks like the thing you'd do if you were a student or bored office worker. Using MS Office and other software to have a laugh and take the piss out of both cheesy pop culture and naff business sales speils. The song chart meme in particular feels like the work of early 20 somethings to mid 30 somethings in its slacker, post The Office (UK and US), smirking, parodic aesthetic. I quite like it too ...
memes remind me of OULIPO, a group of mainly French writers drawn to the idea of la contrainte, constraint, as a means of generating new text. Meme-ing though is multimodal.
One problem with the term meme is that the Dawkins-derived metaphor doesn't assert the primacy of creativity; it is suggests a natural process of self-propagation without human agency.