[HoboSteaux]

This is all very tentative still, but I am planning a Server / HTPC, with Xen running the whole show. I am drawing blanks for many items, so any help is appreciated;

[Linux]

[CPU] i5-2400 (great price/performance mark + AES instructions)
[MOBO] none yet; dual eth when one is released
[GPU] nVidia 530 (if they do the same leap that 460-560 made...)
[RAM] 8-16 gb (vm's are a hog)
[CASE] Silverstone GD04b
[PSU] SeaSonic X-series 400 watt (I have the 750 for my main; best PSU ever)
[Remote] ??
[Mouse/KB] ??

Any input is appreciated

[teaguecl]

Any input is appreciated

This is all too speculative for anyone to comment on other than in generalities. For specific advice, re-post it when the parts you want exist.
As far as general approach, your "big iron" server+htpc is usually not the recommended design. Normally we recommend a small, low power XBMC client in the living room plus a small back-end server running some form of NAS plus any other services you need. I personally love the fanless ION machines, but people who do lots of video streaming need more CPU.