I've searched around, and saw no direct issue being discussed.  I have Vista Home Premium with a ASUS MyCinema PE-9400 ClearQAM Tuner Card.  Now, when I watch TV on my desktop, the clock is fine and never goes out of sync, but when my Xbox 360 is used as a Extender for a long period of time, my clock slowly drops 1 minute every 10-15 minutes.  My brother uses it to watch TV as there is no cable line going into his room.  I noticed the clock going out of sync when he had it on for a long period of time (about 3 hours).  I looked at my clock around 11:30pm, and it said 9:36pm (roughly 2 hours behind).

I'm certain it's not the CMOS battery as again the clock is fine when the Xbox 360 is not connected to my computer as an extender.

Is there anyone that may be having a similar issue with this?

Thanks.

This is not normal behavior.  Although I have had trouble with my clocks losing seconds, I have changed the sync interval with the internet and that has keept my recordings on time.

1.  My gut tells me this is a chipset problem...check for updates to your chipset drivers.  If Intel chipset, google: Intel Chipset drivers and Intel will provide a utility to download and update the drivers.

2.  If that fails, you can change the interval for syncing with an internet clock:

SpecialPollInterval

I updated my chipset drivers.  Before I did, I took a closer look at my system clock, and compared it to one of my other machines, and noticed it took another full second for it to do 1 second.  Basically it took 2 seconds to do one second.

Also it does it continously, not just when the tuner card is active.  Though I did notice it got worse with the tuner card on as well.  I still do not believe it is the battery that keeps my CMOS settings, as the motherboard is brand new (not even 3 months old).  In fact the computer itself is less than 6 months old.

*UPDATE* My computer was in the middle of booting while I was typing this.  So far I'm seeing the clock working better with the updated drivers (not board specific either, but from nVidia's website).  I'll load up VMC, and watch a couple of recorded shows, as well as watch live shows (both caused the clock to slow so I'll do both).

Thanks for the info, as I'll decrease the update interval as well just to make sure my clock stays up to date.

Chipset drivers did not help.  Clock speed has decreased even slower, and again it's when an extender (Xbox 360) is connected.  I'm having to change the sync time to less than 5 minutes, because I lose 1 second every 2 seconds that pass.

I just replaced the CMOS battery to no avail.

Does anyone know the actual cause of this?  Could there be a drain on the computer's internal clock when an extender is connected using the tuner card?