Hi Ryu,
never been to a hostel in my life, but looking at the location it seems you're just a little outside of the city centre.
It is quite a walk to the event-place, so you're best off using public transport to central station. The building where the event is held is right next to central station (If you're standing in front of the central station, with your back to its exit, the party-place is on your right hand in the old looking building). It's actually the same building I work in.
Just noticed the movie "Freddy vs. Jason" is showing on saturday. Anyone want to go and see it on saturday-evening? I heard it's very bad... still want to see it though :-)
In the Netherlands movies are usually in English and have Dutch subtitles, so anyone should be able to understand them I think.
Oh and
here you can find some other info on things you can do in Rotterdam while you're there :-P