have you learn the 'n desu' form yet?
well, as for the second one, it's because "sou" is a -na adj. (isnt it? xD)
like.
-i adj: tanoshii n desu.
-na adj: shinsetsu na n desu.
noun: genki na n desu.
hmm... the -n desu form is like explaining things, i guess.
anyways, hope this helps