450 is plenty.
you wont realy notice the difference between the 6300 and the 6600, they are both good processers with some decent power behind them, and if you want to get some extra power, just ask some people on here, and we will help you overclock.
1gb vs 2gb. depends on if you will be running mem intensive progs, i reccomebd 2gb, but if you plan to upgrade and add mor ram, maybe 1 1gb stick and upgrade with another 1gb later on.
and for the case, any preference in color, window, cd drive bays, desktop or tower, etc...just helps us find a case for u. then again, jsut spend about 2 hours browsing the case section on newegg.com and make sure that it can support a full atx mobo, an easy way to tell, is there is about 6 pci covers.