From your email I read that you're still using an quite old Java version. Do yourself a favour and uninstall this version when LW is completely closed, then reboot and install the newest version of Java (1.5.0_07) using the JRE offline installer from here:
http://java.sun.com/j2se/1.5.0/download.jsp
After you've installed the Java, reboot again.
As for your m4a problem, follow my suggestion above.
