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You can also startup eclipse from the command line with appended -vmargs arguments but I'll leave it to others to outline that procedure.
My IDE:
Eclipse SDK Eclipse Ganymede
Version: 3.1.0 Build id: I20050627-1435
MyEclipse 4.0 M2 4.2
Build id: 20050627-4.0-Milestone-2M20090211-1700
eclipse.ini
location: eclipse/Eclipse.app/Contents/MacOS/eclipse.ini
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