Re: Best way to make my HTPC new game ready
no need for a new build, just change the proc to a X3 or X4. There is little to gain from a newer motherboard/memory.
Limitations for games will be graphic card. What do you plan to play on it? What is your budget? What will fit in your case? How big of a PSU can you fit?
You'll have to accept that you will most probably NOT fit a top of the line GPU in your HTPC. This is not a good fit there... Then again, a 4850 used to play most of last gen games at 1080p for me, so a 5770 may be enough. Check which games you want to play and at what details.
Do you really want a space heater under your TV?
As the universe is curved, there cannot be a straight answer...