Re: your question about Venice hostels from my trip page. There's not much out there. I've stayed twice in private rooms at Foresteria Valdese which is sort of a combination hostel/hotel. The cost was around 60 Euros per night for a two-person room. They have dorms too but I don't know if you can reserve those in advance or not. I would highly recommend la Foresteria--it's super-centrally located in Castello. The other option is the youth hostel on Guidecca, which it is out of Venice itself so you'd have to take the vaparetto to Venice.