Here's a checklist I came up with while reinstalling my HTPC:
  1. Install Vista (I use x64 and manually sliced the disk in a 40GB boot partition, and left the rest for a data/recordings partition).
  2. Allow automatic weekly updates (on Wednesday at 03:00).
  3. Install your network.
  4. Upgrade to latest BIOS (you might wanna skip this).
  5. Uncheck all components in "Control Panel, Programs, Turn Windows Features On or Off".
  6. Install your chipset driver (I installed the Intel package).
  7. Download and install SP1 (choose x86 or x64 and your installed language).
  8. When finished, run vsp1cln.exe to clean up after SP1 installation.
  9. Start Windows Update and install all important updates.
  10. If you have a 2GB 150x USB stick or better, plug it in and configure 512MB for ReadyBoost, and use the rest for timeshifting in your Media Center application.
  11. Right click Computer, then "Manage, Configuration, Services". Set to disabled startup and stop the following services, that is useless on an HTPC:
    1. DFS Replication
    2. Diagnostic Policy Service (change to manual)
    3. Distributed Link Tracking Client
    4. IKE and AuthIP IPsec Keying Modules
    5. IPsec Policy Agent
    6. KtmRm for Distributed Transaction Coordinator
    7. Offline Files
    8. Remote Registry
    9. Tablet PC Input Service
    10. Windows Error Reporting Service
    11. Windows Search
  12. Download and install graphics drivers (I installed ATI's  Driver Only option) 
  13. Download and install TV tuner drivers (I installed Hauppauge's Driver Only option).
  14. Configure your sound card and select your speaker setup. Note Vista comes with a cool  room correction feature you can take advantage of if you have a surround sound setup and a microphone.
  15. Download and install Haali's MetroskaSplitter to support .mkv files (free).
  16. Download and install AC3Filter to support surround sound streams (free).
  17. Open" Programs, AC3Filter, Configuration" and select your speaker setup.
  18. Download and install Cyberlink PowerDVD Ultra 8 to support HD content (commercial app, trial).
  19. Click "Control Panel, Add or Remove User Accounts". Create a standard user with a password, and allow auto logon. Supply the user/password you just created.
  20. Restart.
  21. In the bottom of the Welcome page, uncheck the "Always show..."
  22. Right click desktop then "Properties, Display Settings", then adjust the resolution to match you flat panel screen, typically 1366 x 768 or 1920 x 1080.
  23. Update Windows Experience Index by right click Computer, then "Properties, Windows Experience Index", 
  24. Vista Home does not include Terminal Services. But you can install Mesh and connect the box to your mesh, to enable it.
  25. If you have DVB-C (cable) or DVB-S (satellite), you cannot use Windows Media Center as it only supports DVB-T (terrestrial):
    1. Download and install DVBViewer Pro (commercial app, no trial available).
    2. Launch DVBViewer's options and check fullscreen, always on top and configure your hardware devices and directx filters. Choose the EVR renderer to enable DXVA2.
    3. Download and install EventGhost to support remote control, and this eventghost configuration
    4. Add EventGhost to Startup folder. 
    5. Launch EventGhost and load the configuration. 
    6. Add an action to the Autostart event of type "System, Start Application", executable: "taskkill", parameters: "/f /im ehtray.exe" to prevent Windows Media Center from stealing the remote control commands. If you have no keyboard connected and you are an absolute purist, you could also add "taskkill", "/f /im explorer.exe" to shut down the Windows Explorer and free up extra resources.
  26. Activate Windows.
  27. Enjoy!