Guess I can only use the old case now and go from there but doesn't New Egg have PC builder kits?
I've probably built > 30 pcs - its not extremely challenging (but I doubt you'll find it simple your first time around). As someone who's reused cases before, I generally recommend just starting from scratch and getting a new case. You can typically find something that will be much better than your original case for $20-$30 and might even include a low end power supply. Or if you decide you are going to be a do it yourselfer and want to reuse a case over and over, then I'd suggest dumping some money into a really nice case that is easy to open/close, good ventilation, etc.
Places like new egg, microcenter, tiger direct all have "barebone" kits. These typically are just a motherboard and a compatible cpu, but often include ram and a few other goodies. If you have a local microcenter, I'd strongly suggest heading over there on a scouting mission and get some info from them.
All of that said, GCFL, hope you continue to enjoy your new pc!