The power supply is important (you find this out when a power supply goes poo and your motherboard smokes and flames--I found out the hard way). What it claims as far as wattage isn't as important as what it can really deliver. The Antec cases generally come with a an Antec PSU (power supply unit), and Antec is fairly univerally regarded as one of the best PSU vendors.
Look around for case and power supply reviews, both here (Anandtech) and some other sites. Tom's Hardware is good site as well. Generally something that rates good at both sites is actually good. Check in the forums over at broadbandreports.com as well, there's some knowledgeable folks there.
Personally, I just did a build for someone with the Sonata case by Antec. Nice looking (in a....refined manner), fairly quiet as well. The Overture is it's little brother, pretty sleek looking as well. If you're looking a little more over the top, my best bet would be to be one of the fairly dull looking Antecs (maybe with the window already in) and look around the modding sites and do your best (or worst) to it. That way it won't just be the same "extreme unique" case that everyone else has.
Good luck and don't push that hard, if something isn't going, take a step back and make sure you're putting it together properly. Oh, and leave the side-panel off when you power it up the first time. I guarantee if you don't, you forgot something, and half your front panel connectors are plugged in wrong.
:beer: