the song used in the beginning is:

The Mortal Coil - Song To The Siren

What about the tune at the end just after the chainsaw comes through the wall?

The song is Signal to Noise by Peter Gabriel, it isn't the album version though. It was used also in the opeing fight sequence in Gangs of New York. If you want to find out music from a trailer, a good site I found is www.soundtrack.net. Click on the sources link and there is a huge list of movie trailers to look through.