I have got Vista SP1 and TV Pack 2008 on a Vaio with NVidia 8500GT graphics and Hauppauge WinTV HD-S2. I tried to install the hacked MSDTVVDEC.DLL file and had problems with messages such as "dllunregisterserver error code 0x80070005. So I did the whole thing in Safe mode and it seemed to work.
Anyway, after installing it, none of my TV channels could be accessed any more, SD or HD. It said the Video codec was missing or something...
So moved the old DLL file back, did a system restore, and I'm back to viewing SD channels again. So what did I do wrong?
UPDATE - Success!
I did it all again and it's worked!
The only difference was that last time I entered the command instructions under safe mode, whereas this time I entered them by executing the "Run" command as an administrator (which is what the instructions say.....)