How do I connect 2 buildings networks?

At our office we recently rented more space but the space we needed is at a physicaly seperated building across the street from our building. Both locations have dsl connections with static ips. I would like to know what would be the most economicalway to link these buildings. There is one computer in our new building and a peer to peer network in our old building consisting of 5 computers. My boss does not want to use any of the pcanywhere or laplink type software to link them what should I do?