Hi,
First post, so here goes .. I have a Philips MCP9350i media centre (don't all boo at once) running XP and media centre 2005. For a month or so it's been working fine, until I decided that the dodgy lipsyncing drove me mad enough to try and install a better driver (it was like watching a badly made 1970's Chinese KungFu movie in the shape of the BBC news) 
In an effort to sort out the lipsyncing issue I foolishly decided to update the driver for the dual tuner. I downloaded the Nvidia DualTV Full install for MCE 2005 (V1.34) from the Nvidia site. Download was successful so I ran the install file, I got a screen asking for the original activation key "found on the cover of your original installation CD".
The problem is, I don't have the original installation CD. The system was bought new last year and doesn't come with any media at all, it relies on a restore boot sector on the HD. I was about to give up on that, when I looked in the newly created Nvidia directory on the C:\ drive and saw what I thought were the right drivers .. so .. .. I went into device manager and tried to manually update the drivers .. this gave me the "blue screen of death" and the unit rebooted itself. When it finally booted, I clicked on "live TV" and it worked !! 
I found I had 2 entries for the DualTV hardware in device manager, I looked at the driver versions for both entries and they were both different - one was dated 2005, the other 2006.
I should have left that as it was, as I could watch "live TV" without any problems - instead I tried to update the older driver (2005) to the newer driver (dated 2006). This caused my now familiar blue screen (in MCE 2005) that says "No TV tuner detected, please install or set-up correctly".
While "live TV" does not work, I can still watch recorded programmes - no problem.
I've tried going back and updating the dualTV tuner with the standard "Philips" drivers - no joy - still get tuner not detected
Tried removing the dualTV tuner using device manager - sometimes it lets me remove it, sometimes it doesn't - then I install the hardware manually using "add hardware" in "control panel" still no joy - tuner not detected.
Tried using system restore to go back to a time when all was fine and dandy - no joy - still get tuner not detected (tried this a lot with different dates in the past).
Finally decided last night to invoke the "Philips system restore" utility as a last resort, so after backing up all my important files, I hit the F11 key as instructed during boot up, followed the on-screen instruction to the letter - and voila .. .. .. still get the infamous "tuner not detected"
I shut it all down, resigned myself to the fact that is wasn't going to work, unplugged it, had a stiff drink, then decided to have "just one more go" at getting my "live TV" back again - plugged it all back in again, removed the tuner using "device manager", then loaded the standard Philips "out of the box" driver and it worked !! - I made a "system restore" point straight away, then proceeded to record a programme. I wanted to watch another channel and it told me that I would have to stop the recording to watch the different channel (I could always do this when it was originally working before). So to make the "other" tuner visible I did a "scan for hardware changes" in "device manager" - and guess what .. .. I'm back to the "tuner not detected" message again 
Haven't tried to roll-back to the working system restore point I created last night when it was working .. that's a job for tonight ..
I bought the unit from PC World just under a year ago, got about 3 weeks to run on the warranty, so the clock is ticking (if the tuner card is faulty I need to let them know ASAP) .. (Which also means that I can't open her up and have a look inside, to add memory, upgrade the HD etc - that will be a little job after the warranty expires 
Questions
(1) Have I downloaded the correct Nvidia driver - and if so, how can I obtain a valid installation key, do I need to buy one ?
(2) Could the dualTV card be faulty - is there any diagnostic software that I can download to check it out ?
(3) Should I just bin it and buy a generic HDD DVD recorder ?
(4) Should I see two entries for this tuner in "device manager" ??
(5) Is this really just a "buggy" bit of hardware (the MCP9350i or the DualTV tuner)
Seriously contemplating buying a video recorder again 
Any help, suggestions or advice would be greatly appreciated ..
Cheers - TC