A couple of things. Does your brother also have MSM installed. It wont work if he does not. Are any of you behind a firewall as this can cause problems.
If you both have MSM and a hotmail account then you should be able to connect to him but puting him on to your contact list and then click on start net meeting. If he hasn't got a hotmail account then yu'll need to key in his IP address on the top bar.