I did exactly what you're thinking of doing about six months ago. I didn't build a room for it, but I did build the "computer" part of the Media "room" I am planning to end up with. I went all out, and went to an OS I have never used before Ubuntu. I'm a computer support tech so I built everything from the ground up. I purchased 4 2tb Harddrives and used Ubuntu to create an RAID5 Array. I ended up with 5.2tb of Harddrive space.
I used a separate Mirror array for Ubuntu and XBMC.
I'll break my Hardware down into sections of requirements. But it was all considered as a whole unit when I was building it all.
TV is a 50Inch Plasma Full 1080p Resolution.
Sound System is a DTS/Dolby Pro Logic Receiver (5.1) It's old but sounds great still, I will probably upgrade this next to 7.1, but the moment it's great.
Speakers are Setup around the room typical 5.1 setup.
PC Requirements:- This is actually an old PC I had, but it was by far enough power to handle all of this. I have yet to notice any slowdown or performance issues, even when copying 50GB across Wireless from it etc.
Case - GIGABYTE 3D Aurora Black Aluminum ATX Full Tower Computer Case (Spare care I had)
PSU - 700W Modular High Performance Power Supply
Mobo - GIGABYTE NVIDIA nForce4 SLI ATX AMD Motherboard with 1394b
CPU - AMD Athlon 64 X2 4600+ Manchester 2.4GHz Socket 939 Dual-Core Processor
RAM - G.SKILL 2GB (2 x 1GB) 184-Pin DDR SDRAM DDR 400 (Upgraded from 1GB I had in there)
OS Drive x2 - Seagate Momentus 500GB 7200 RPM 16MB Cache 2.5" SATA 3.0Gb/s Internal Notebook Hard Drive
I used two 2.5 Inch drives in the middle slot of the RAID Array because I wanted easier airflow across the RAID5 drives. These where purchased as well since it only had 80GB IDE Drives at the time.
RAID Array Requirements:-
RAID Controller - HighPoint RocketRAID 640 PCI-Express 2.0 x4 SATA III (6.0Gb/s) Controller Card
Drive Bays - StarTech SATSASBAY3BK 3 Drive 2.5"/3.5" Removable Mobile Rack SAS/SATA Backplane
Drives x4 - HITACHI Deskstar 2TB 7200 RPM 64MB Cache SATA 6.0Gb/s
Media Center Requirements:-
Audio - ASUS Xonar D1 7.1 Channels 24-bit 192KHz PCI Interface Sound Card
Video - PNY Verto GeForce 210 1GB 128-bit DDR2 PCI Express 2.0 x16 HDCP Ready
Network - Zonet ZEW1690 Wireless Adapter with Dual 7dbi Hi-Gain Antenna IEEE 802.11b/g/n
CD Reader - LG Black 10X BD-ROM 16X DVD-ROM 48X CD-ROM SATA Internal 12X Internal Blu-ray Drive 3D Playback
Home Network:-
Rather complex Dual cable model setup with about 20 devices, it has multiple wireless APs and domains etc. It is Gigabit and but this is the Wireless Part for the Media Center.
Wireless AP - D-Link DIR-825 Gigabit Gaming Router 2.4/5GHz Simultaneous Dual Band Xtreme N600 Router
My only real regret is the Video Card, but I paid $25 for it, at the time of building there was very very little choice of full sized HDMI Output cards. When playing movies or videos even full high-def BluRAY movies there is no issue, but sometimes the interface bogs down a little. Though with Eden it has yet to do so, I recently purchased the BluRay reader, and it works great, originally it was just the old DVD Drive I had in there, wasn't even SATA lol.
I had Three issues.
The Wireless network card is the largest of them all. Wireless was required because where the TV was is in an unusual place and running network cables to it was not really an option without remodeling 1/4 of the house. That will change once I get my room setup/finished but for the moment it's wireless. It actually worked out really well because I was able to finally put my DirecTV DVR on the internet by using Ubuntu as the router. Plugged the DVR into the LAN port on the PC and shared it's network. The issue is Ubuntu, it was probably not the best choice when it came to Wireless, every time the headers get upgraded I lose Wireless, and have to run a simple 4 line bat file to get Wireless back. It was also the most difficult to setup because it required alterations of the code and recompiling the driver etc. It was a learning experience and one that threw me into Ubuntu style of understanding etc. It may have been a pain in the behind, but I am better for having the experience.
The RAID Array also gave a very small amount of issues getting it installed initially, but once I understood what needed to be done it has worked flawlessly, this was lack of knowledge in how Ubuntu works on my behalf rather than the hardware. It has yet to fail and I've reinstalled Ubuntu twice on the media center (Originally went with a cut down version, then server, then just stuck with Desktop) And the second and third times I had no issues.
The sound card was a little challenging mostly on XBMC's side rather than Ubuntu. Ubuntu sees it and uses it, XBMC had issues and it took a lot of effort and searching to work out what the issue was. Eventually I came across a thread on this forum that helped out an incredible amount. Once I worked out what XBMC was looking for, I've had digital media play though HDMI or the Sound System with ease.
As a side note that sound card is worth it's weight in Rhodium, it's abilities and quality are outstanding.
I've been meaning to do a "Project" type posting to help people who may want to get into XBMC with Ubuntu because I think I've learnt so much and retained it I can problem solve. There is a couple of small issues but no real central repository for the common issues associated with XBMC on Ubuntu for example. You kind of have to look though the Ubuntu forums AND the XBMC forums, suck in all the data and come up with a solution.
I went from not ever installing or touching Linux based OSes apart from downloading the CD before, to a fully blown, Media Center, Network Routing, Archiving/Backup options server, using both old and new hardware.
Don't get me wrong it was a good two weeks of building, reading, google searching answers. I've even started to turn my older laptop into an Ubuntu laptop and running XBMC.
By the way, since my main Laptop is always open next to my recliner, I use the computer to control XBMC. No, not with VNC, but a No Screen displayed version of VNC. It basically just pumps the mouse/keyboard input to Ubuntu, where XBMC picks it up. I'll get the tool name if anyone is interested, it runs on Window 7 64bit and basically turns allows me to move my mouse over to the right-hand side of the screen, which then starts the move the mouse on Ubuntu. Once there anything I type or do on the Keyboard/mouse is piped to Ubuntu only. To get back to Win 7 I just move the mouse back onto the Win 7 screen. It's really kind of sweet.