a couple of things.
you have to remember that the htpc cases are MUCH smaller, so something that would produce a reasonable amount of heat ina large case could be a problem in a small area like this.
I went with a passive graphics card (gigabyte 7600gt) and the heat from it when its not actually doing anything is incredible, seriously! And also, the conroe and the mosfets round the cpu socket, the northbridge and southbridge all give off a good (bad) amount of heat, and in a tiny enclosed space, it soon becomes a mini oven.
Air flow is a must, even if it is just moving the air around so that the extracting fans can do their work.
all your bits look fine, and thats a good psu, but you may find that the spare wires get in the way, i did, so i have gone with a modular psu (enermax liberty).
quietest drives are the samsungs.
The silverstone looks a decent enough cooler, but it takes 60mm fans, and for the airflow that they produce, arent quiet. I bought a scythe mine, but that was too tall, so i have gone for a Thermalright s1-128 which should give some cooling to the area round the cpu and also the ram. Ill let you know tomorrow