Hello Chazbaps...
If the advert is the one where a guy is walking around a field (picnic?) and people keep on appearing etc, the song is called "Little Yellow Spider" and is by the wonderful Devendra Banhart.
It is from his album "Nino Rojo" which i thoroughly recommend getting. Also check out the album "Rejoicing in the Hands" and his latest, "Cripple Crow". All superb!
For more, have a looksee here...
http://en.wikipedia.org/wiki/Devendra_Banhart
Hope this helps!