There are many ways to skin this cat, many I don't know much about. I simply use pcanywhere. You didn't mention how your LAN connects to the internet, but if through the SME server, do this:
1. In your server, forward ports 5631 and 5632, both tcp and udp to the fixed ip address of some windows box on your network.
2. Set up pcanywhere host on that box, with a username and password, and all the max security options and encryption.
2. If you have a fixed ip for your SME server from your isp, then remotely point pcanywhere on your laptop to that ip, and in a few seconds, you will be sitting at the console of the box you set up in step #2. You can now open and run MYOB, and it will be as fast as your slowest link in your internet connection.. Generally, for running an application, this is the fastest way to get the job done, as you are only using the communication link to transmit keystrokes and changes to the screen display.
If you use a router to connect your LAN to the internet, then program it to do the port forwarding as above, and leave your SME server alone.
If you do not have a fixed ip address from your isp, then set up dyndns or equivalent on your SME server (see the docs for how to do this). You will then point your laptop pcanywhere to the dyndns address you have established, and again you will sitting at your assigned system on your local network.
If you were to try to run MYOB on your laptop, and open the data files on your SME server, (perhaps using a VPN connection) even with a seriously fast internet connection all the way, you would find the response time to be like turtles swimming through peanut butter.
Hope this helps,
Tom