Open the file in text editor (bbedit) and set the memory values:
-vmargs
-Dosgi.splashLocation=/Applications/Eclipse/MyEclipse/MyEclipse 5.0GA/
eclipse/MyEclipseSplash.bmp
-Xdock:icon=../Resources/Eclipse.icns
-XstartOnFirstThread
-Xbootclasspath/p:../../../plugins/
org.eclipse.jdt.debug_3.2.0.v20060605/jdi.jar
-Xms128m
-Xmx512m
-XX:PermSize=128m
-XX:MaxPermSize=256m
-Dcom.sun.management.jmxremote
-Dorg.eclipse.swt.internal.carbon.smallFonts
-Dorg.eclipse.swt.internal.carbon.noFocusRing