A matter of choice
Every week I receive a few email messages from Readers who ask my advice about choosing between these two cameras. Frankly, I cannot give you a clear recommendation.
If you think you really need image stabilization, then you have to get the the E-510. Just don't be surprised if this does not solve all your problems with blurry pictures in low light.
If this is not the case, the choice becomes a matter of personal preference. Both cameras deliver equally good images, both share the same features and adjustments. The simplification of user interface in the E-410 is a plus, but you may be among the (very) few people who will miss the removed external controls or preference options. On the other hand, the 85 g difference in weight may be an advantage of the E-410 if you like to travel really light; so may be its flat body shape, if you like the traditional (non-grip) classic film cameras of the past.
If this did not help you to make your mind, visit a local camera store and try how both cameras feel in your hands, then follow your intuition. In either case, you will not regret your choice.