Ok this is going to be my first attempt at a HTPC Build, the main reason is so I can have an all in one system that I can give as a present to my mum. Ive got a budget of around £600 but would like to spend in the region of £450-£550. IVe done a bit of research into HTPC's and this is the current set up im considering. Ive also given the average price. Ill use the newegg links just because it's easiest.
I would go with an AMD setup for a HTPC if it was me. I would also consider going with a bigger HD since you're getting a tv tuner card. I can't seem to ever have enough storage space in my HTPC. I currently have about 2TB of storage and am looking at adding more. I would also consider getting more RAM since RAM is so cheap right now. I would get 4GB and use Windows 7.
I recently upgraded my HTPC from Vista to Windows 7 and have been very happy with the results. I was able to get Vista to work, but had to do some hacks to get it to recognize both of my tv tuners and to tune sub-channels. Windows 7 just worked out of the box with no tweaks.