Since you have some answers already which provide links to system builders I'm going to offer an alternative.
In the question you linked to I provided an answer which reflects my current leanings on the subject: a centralized, powerful server provides content to less powerful units at the TVs.
In your case I would suggest buying as powerful a central machine as you can for around $600 (which gets a lot these days, particularly on AMD's platform) and an XBox(for running XBMC at the TV) or XBox 360. In the end you'll have spent roughly $1000 (USD) and have the foundation for an expandable system and a gaming console. That is assuming you don't already have an XBox at which point you'd be your leveraging existing hardware and can put more power, additional tuners and more drives into your central server.
This method has several advantages:
The central server does not need to
be in an HTPC case which can be
expensive if you value quality and
The noise of a powerful system
(spinning drives, fans, etc.) is
moved away from the viewing room
without the added cost of higher
quality parts and sound deadening.
You can increase the number of TVs which can access the central machine's content very cheaply as the client machines do not need the beefy harddrives, tuner cards or excesive amounts of RAM (see for example, an MSI Wind which can be configured with built in wifi, HDMI and can run WinXP Media Center Edition or Windows 7 for around $300, or an AppleTV which ranges from $230 to $330, has wireless N support and HDMI)
*A Playstation3 can be used out of the box as a Media Center and even has a Blu Ray player in it, but it cannot run XBMC which is a much nicer and more versatile interface. And forget web surfing from a PS3. Its a terrible user experience.