My real questions are:
--Is there a simpler solution for my needs? -maybe using an Asus EeeBox, or Hauppage, or SiliconDust, or another stand-alone unit?
--Would using micro-Atx be simpler, cheaper, or quieter?
--Will using an SSD instead of a HDD and recording onto a network drive really make much of a difference in boot time, temperature, or noise level?
--Will it be easier to control basic functions with the tuner remote, Gyration remote, another MCE remote, or a universal IR remote?
--How much RAM and PSU wattage is enough?
--How do I know that Win7 will find all of the channels in my cable package?
--If I install WinXP first, can I use an upgrade version of Win7?
1. if you mean simpler than assembling your own HTPC, for sure. A ready-built PC is simpler, and a stand-alone box is probably simpler still, but can't advise exactly what. You listed the Eeebox -- a PC -- and two brands of TV tuners for PCs... so not sure what you're suggesting as a n alternative. A HTPC is more complex than a stand-alone box... and you won't find any PC to turn on in 10s (except from sleep).
2. probably. mATX is cheaper, can use bigger heatsink & quieter fan
3. yes, SSD will boot faster but not 10s and it depends on how much software you have loaded -- and it will definitely be quieter, if the rest of your components don't make more noise than the drive
4. can't answer
5. RAM is cheap, but 2gb shoul be plenty. Power -- you don't need much, real consumption would be no more than 50-60W most of the time.
6. no answer
7. don't think so. I'd start with win7 if that's what you're going to end up with. save the hassles of loading the OS twice.
other points --
That case & psu looks a bit like the http://www.silentpcreview.com/apex-mi008
-- but it's not been reviewed and no one here has used it, afaik. hope that the PSU is quiet.
Personally, I don't trust Atom with any chipset to be an effective media PC. The CPU is just too anemic for me. Even if the HD video is OK, you still have to navigate through menus, databases of files, etc... A low end 45W AMD dualcore & 780/785 mATX mobo would give you much better performance & be cheaper.