Please refer to:
http://www.netbeans.org/kb/41/using-netbeans/configuring.html#switches From the documentation:
You can add startup switches to the
IDE on the command line or by entering
them in a special file called netbeans.conf, which is located in the etc
folder. You can enter IDE-specific startup switches and pass arguments
directly to the JVM in which the IDE runs.
For example, to set the -Xmx (maximum heap size) for the JVM in which the
IDE runs, either add the line -J-Xmx64m to your netbeans.conf file...