can anyone tell me how to set up 4 computers on a network and play over the internet on a 1.5 kbps adsl connection with no lag
Limit the upload and download speed of each machine to 20% of what the connection is capable of, as it will only ever sit at 80% load (max) inbound and outbound responce (ping / latency) will be better.
As the up/down stream side of the link is not saturated ACK packets will also be able to get through, and throughput may also increase.
www.netlimiter.com
You should consider a ADSL router with QoS for each client.