I am in a similar situation of trying to learn a little of the language before I move to Switzerland. I have five years of German under my belt, although I have never yet been in the position to use it in everyday situations.

That being said, I am currently trying to refresh my German whilst simultaneously learning as much Swiss German as possible. Ho boy! It's a different language alright! The Swiss German is messing up my High German and vice versa. Every time I try to speak in one, the other comes out, and since I only have a smattering of Swiss, I finish sentences and phrases in High German.

My advice based on this experience is to focus on one or the other, rather than learning High German and hoping to pick up SG in Zurich. They're similar enough to get REALLY confusing if learning both.

Also, if you want to get a jump-start on learning Swiss German, there are some good learning aides that you can get relatively easily. Pimsleur makes a Swiss German audio set. I also bought a copy of Dr Chly Prinz direct from the translator and have been reading it alongside the English translation (The Little Prince). My personal favorite is a book that is made to go along with the Swiss-made movie Die Schweizermacher (which you can get by googling the movie title). That one is good because the movie itself is a parody of Swiss culture.