However I want to build a server/HTPC combo but I am a silence freak, specially when it comes time to sleep, I can't get a good nights sleep with a constant humming in the background. Also I traveling so I will need to have it as small form factor as possible.

Would it be possible to build a system with these criteria:
1. Portable Mini ITX form factor
2. Completely passively cooled

So far my plans are to use
M350 Universal Mini-ITX Enclosure
External PSU silent power brick
A solid state drive

And my plans were to use the Zotac IONITX-C-U but the temperatures measured in the xbitlabs dor com/articles/mainboards/display/zotac-ion-itx-c_7.htmlxbitlabs review of the motherboard seems too high to feasibly use it passively cooled... Or is it?

Presumably, you refer to this case:
http://www.mini-box.com/M350-universal- ... -enclosure

It does not look ideal for passive cooling, but rather, low airflow cooling. Convection will not cool enough w/o massive heatsink area, which is not feasible in such small case. But a samll amount of airflow is enough to drop temps by large margins for low power CPU/chipset.

Rethink. Consider low profile quiet fan coolers. If you want passive, go to a heatpipe-heatsink style case designed specifically for it --

http://www.silentpcreview.com/Coolermas ... i-ITX_case
http://www.silentpcreview.com/mCubed_HFX_Micro

ps -- if the system is running just one quiet fan, unless it vibrates a lot, there won't be a hum; that is most often caused by a HDD making the chassis vibrate (90 or 120Hz & harmonics)

What CPU and GPU power you need.
The one that will work with that case with no fan is an atom N270 board the mobile version of atom board Intel D945GSEJT you can find this at about 120$ and the power supply is on the motherboard so you only need a small 12V brick (the board only require max 12W)
If you need more power then you will need a fan or a much more expensive and heavier case.
If you want to buy an SSD check the spec carefully some are using 3 to 4 times more power than others I have a Samsung 32GB only 0.42W max

Like this (plus ssd):

http://homepage.ntlworld.com/bill_todd/PVR/passive.html