Hardware: Standby Issues

I currently run Windows XP Media Centre Edition on my Alienware m9750 laptop. When it's plugged in it will quite happily standby into S3 (suspend to RAM). I had to add a registry key (USBBIOSx) to make it wake up from Standby with USB since the BIOS doesn't have a setting to wake up from USB. The problem is that it now won't go into Standby when on battery power. Or rather, it will, and the instant it does it wakes up again.

Any ideas? Other than "Leave it plugged in"? I'd like to see my power adaptor continue to work for quite some time so I tend to unplug it most of the time and plug in only when I need to charge the battery. Naturally, when the computer is in S3 mode it uses hardly any power so I don't want to have it plugged in to be on standby!

I deleted the registry key and now it does go into Standby but obviously now it won't wake up on USB activity. Grr.

It's the other way round. If I go into standby and then unplug the power it wakes up immediately.

Posted By: Spode

Ok, so what happens in the following situations?

Power In Standby, Power In Wake Up
Power In Standby, Battery Wake Up

Battery Standby, Battery Wake up
Battery Standby, Power In Wake up

Currently (without USBBIOSx) everything works as you might expect except that you need to press the power button to wake up from Standby.

With USBBIOSx:

Power Standby, Power Wakeup is OK
Power Standby, Battery Wakeup isn't: as soon as you unplug the power it wakes up
Battery Standby: As soon as you go into Standby it wakes up again immediately.

I would rather like to be able to press any key on my USB keyboard to wake up from standby but I can't do that without the power in at all times because I need to enable USBBIOSx.

Vista behaves perfectly well, on the other hand, so this is perhaps something unique to XP (or perhaps even unique to MCE).