Upgrading Java won't help at all with this.
Make sure your display drivers are up to date. And make sure in the Mythruna display setting that you leave AA set to disabled.
What kind of graphics card do you have? Or you can just post the whole error log since it has that info in it as well as the settings that you used.
I don't know what kind of graphics card I have and the laptop i play on is a dell inspiron 1501 if that's any help.On a more precise note, here's the error log from the client text folder:
2012-03-26 11:35:49,671 ERROR [mythruna.client.MainStart] Unhandled error:Failed to create display
org.lwjgl.LWJGLException: Failed to find ARB pixel format 1 0
at org.lwjgl.opengl.WindowsPeerInfo.nChoosePixelFormat(Native Method)
at org.lwjgl.opengl.WindowsPeerInfo.choosePixelFormat(WindowsPeerInfo.java:52)
at org.lwjgl.opengl.WindowsDisplay.createWindow(WindowsDisplay.java:210)
at org.lwjgl.opengl.Display.createWindow(Display.java:306)
at org.lwjgl.opengl.Display.create(Display.java:873)
at org.lwjgl.opengl.Display.create(Display.java:782)
at com.jme3.system.lwjgl.LwjglDisplay.createContext(LwjglDisplay.java:137)
at com.jme3.system.lwjgl.LwjglAbstractDisplay.initInThread(LwjglAbstractDisplay.java:113)
at com.jme3.system.lwjgl.LwjglAbstractDisplay.run(LwjglAbstractDisplay.java:205)
at java.lang.Thread.run(Unknown Source)
2012-03-26 11:35:49,671 ERROR [com.jme3.app.Application] Failed to create display
org.lwjgl.LWJGLException: Failed to find ARB pixel format 1 0
at org.lwjgl.opengl.WindowsPeerInfo.nChoosePixelFormat(Native Method)
at org.lwjgl.opengl.WindowsPeerInfo.choosePixelFormat(WindowsPeerInfo.java:52)
at org.lwjgl.opengl.WindowsDisplay.createWindow(WindowsDisplay.java:210)
at org.lwjgl.opengl.Display.createWindow(Display.java:306)
at org.lwjgl.opengl.Display.create(Display.java:873)
at org.lwjgl.opengl.Display.create(Display.java:782)
at com.jme3.system.lwjgl.LwjglDisplay.createContext(LwjglDisplay.java:137)
at com.jme3.system.lwjgl.LwjglAbstractDisplay.initInThread(LwjglAbstractDisplay.java:113)
at com.jme3.system.lwjgl.LwjglAbstractDisplay.run(LwjglAbstractDisplay.java:205)
at java.lang.Thread.run(Unknown Source)
2012-03-26 11:35:49,671 ERROR [mythruna.client.MainStart] Default handling did not exit.