Just provide them as command line parameters to eclipse
Best place to do this is in the shortcut to myEclipse
You’ll see something like this in the shortcut properties:
C:\eclipse\eclipse.exe -vmargs -Duser.language=en -Xmx512M -Dosgi.splashLocation=”C:\Program Files\MyEclipse\eclipse\MyEclipseSplash.bmp”
Just increase the -Xmx512M to higher number
You can also add –Xms128M or any higher value
These are actually java vm parameters. see http://java.sun.com/j2se/1.4.2/docs/tooldocs/windows/java.html