Wez Griffin:

Defintly. Thanks bdo. So let me get this straight. If I have one of these connected to my network, and I have two Vista Media Centres on the same network, they will share the 2 tuners correctly. What i mean by that is, that if one computer is watching a show and recording a show (thus using both tuners) and then someone on the other computer tries to watch TV, will VMC tell you that the tuners are both in use or will it just steal the tuner from the other computer???

Used to be, but not anymore.
The latest firmware rev for the HDHR enables 'tuner locking':  If a tuner is in use, it's locked to the system that grabbed it first, and will remain locked for (IIRC) 5 minutes after usage is stopped (e.g. exit LiveTV, or recording stops.)  The other MC should receive a 'no TV signal' error.
But, all that would only happen if you configured each Media Center to use both tuners, rather than configuring one MC to use Tuner0, and the other to use Tuner1 (unchecking the second tuner when you run TV Setup.)

HDHomeRun DVB-T is now available in the UK from pcTVok.com - cost is £ 159 including VAT and next day delivery