Sounds good! I don't have Lego mindstorms myself, but I could help you with your scripts.

First you need to get the Java Communications API for serial port communication working. Sun's version of it for Windows seems to have disappeared from http://java.sun.com/products/javacomm/, but it's still available here:
https://sdlc2d.sun.com:443/ECom/EComActionServlet;jsessionid=95A4C22FD58D3564EFB29CD0DB66474B
But download soon, because it might disappear as well.

So the first step is to get the javacomm stuff installed and running. Then you can download the RCX library and add it to Scriptographer/java/lib, reload the plugin and start coding.

As a starting point, please try this:

var rcx = Packages.rcx;
var port = new rcx.RCXPort("COM1");
rcx.Motor.A.forward();
rcx.Motor.A.stop();
port.beep();
println("Battery Level = "+port.getBatteryPower()+" volts.");

Good luck!