um...
I'm pretty sure there weren't any remixes of "United Snakes"
the only released version is the instrumental one, and it's the b-side to "False Flags"
http://www.discogs.com/Massive-Attac...s/master/32698
now - when they played it live... a few times 3D did add vocals, etc etc etc
and about "Collected"
YOU ABSOLUTELY SHOULD GET THE TWO DISC VERSION
it has a few new and unreleased songs
stuff that's actually legitimately rare
(edit)
here's the Amazon link to it
http://www.amazon.com/Collected-Mass...5012409&sr=8-1
sure - it is a bit pricey now (even for a used copy)
but essentially you're getting a double album and a dvd