I think that is a good news and I am only half surprised.
Since the creation of Beolounge, B&O does not have a community site where people can discuss, and it was very appearant that they decided to remove their discussion forum because they could not/did not want to compete with Beoworld. And now even better, they want to support us. Great.
- Banners (static or flash, but silent and not intrusive) would obviously be a good option. The advert at the bottom of the page are never seen, so it I would suggest rotating banners at the top.
- Having some of the monthly prizes donated by B&O is great, and for those prizes, in the prize section and in the prize thread, you can say "offered by B&O" and link to their site to the corresponding product page.
- In the news articles, you can repeat their press releases or their annoucements, but quoted as such ("B&O has made the following announcement today....")
I suggest you do not do product reviews as part of the deal (it does not mean you should not do product reviews at all). If the review is good there will be some Beoworlder that will say you've been bought and if the review is bad, B&O will be unhappy.
I also strongly suggest you do not create paid-for threads as part of the deal. Let's say you create a thread about the BV8-40. Inevitably there will be some negative user comments, as there is always in an open discussion, and B&O will not like their advertised product directly associate with the criticism.
In other word, all the advertisement should be separated from the site content. And B&O and Beoworlders will be happier.
p.