The sentence is phrased the way it is to avoid unnecessary repetition. It'd be like saying "Whose computer is this computer?" By saying だれの, it's essentially leaving the noun that's intended to follow it implied.
It seems to work now :). I agree with others that "Whose PC is this?" is more natural English, however I like "Whose is this PC" since the more literal translation helps me remember the Japanese better.
There is a subtle difference between the katakana for "so" and "n." For "so," as in "paso," the kana is ソ, while for "n" as in "con," the kana is ン. So, for example, a word with the roumaji "son" would be written in katakana as "ソン"