In answer to your question, a 300 watt PSU is strong enough for the system you've put together. However, you should get a stronger one if you ever plan to upgrade to a Radeon 9700 or better graphics card.
Not sure how much that case costs, but Enermax makes a few cases of similar design. Maybe you should take a look at some of <A HREF="http://www.newegg.com/app/listProduct.asp?DEPA=1&submit=manufactory&catalog=7&manufactory=1400&description= " target="_new">these</A> and see if you like any of them.
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