This is my first post, but I've been through 3 cases, 3 motherboards, 2 cpus and 3 different optical drives and I'm not at my final configuration for a decent media PC, so thought I'd share my own experiences. (All my own fault - I made some hasty decisions and didn't research the products well enough)

Have you thought about power consumption and noise?

Getting a gigabyte mobo with built in graphics, HDMI and an energy efficient CPU is a good option to reduce power consumption and heat in the box. This is what I bought... (in the end - first solution was intel with 2 different mobos - the first didn't support vista properly so had to bin that and start again)

1 x Gigabyte GA-MA78GM-S2H 780G Socket AM2+ onboard VGA 8 channel audio mATX Motherboard 142347  £46.44
1 x AMD Athlon 64 X2 4850e 2.5GHz Socket AM2 Energy Efficient 1MB L2 Cache Retail Boxed Processor 144638  £47.04

That's from www.ebuyer.com (obviously UK, but if you can find the same in NZ then it's a fantastically cheap combination). The CPU is only meant to draw 45 W in total and the mobo onboard graphics is rated to decode HD (h.264) as well (although read the below post about this...)

http://www.geekzone.co.nz/forums.asp?ForumId=84&TopicId=24816

I had an antec fusion at first and I have to say they are very well designed cases. The fans are huge and very very quiet AND efficient due to their sheer size so you can get away without putting a fan on the CPU cooler (which by the way - if you buy a retail version of the athlon, the stock cooler is fine!).

Not having an extra graphics card on the mobo means less heat as well and more room for airflow in the case (it's quite cramped in the antec).

There's nothing wrong with the fusion, but in the end I changed it for a zalman hd135 for several reasons, mainly because it was full hifi width and sat on beneath my AMP better. It also has a built in IR port, whereas with fusion you have to run an ir receiver from the back or somewhere. However, it's much noisier than the antec - really noisy. The insides are no where near as well thought out and the all aluminium construction amplifies all the vibrations in the case. So, I don't think there's anything wrong with the fusion.

With regards to DVD player - make sure the speed can be controlled by speed management software - otherwise you may end up with a very noisy dvd player. I've just got LG GCC-H20L combined blu-ray and hd-dvd player (only 60 quid in the UK) but it's rubbish - it makes a terrible racket when you play back DVDs and it doesn't respond to speed management software. So I'll have to transfer that to my normal PC and buy a LiteOn DH-4O1S-10C instead which is meant to be much better (but more expensive).
Consider getting a blu-ray drive though - if you want to future proof your HTPC for a couple of years :-)

I'm sure I read somewhere that 1x 2GB might mean less heat than 2 x 1GB but don't think it'll make that much difference. You're also meant to be able to get marginally better performance from 2 x 1GB, but since the bottle neck on most systems is the HDD, I doubt it'll make that much difference.

I've also got vista 32 home premium on my HTPC - turn off all the pointless extras such as Windows Defender, Sidebar, Indexing, Firewall and it'll speed up the boot time and reduce disk chugging.

Hope this helps.

Reg