I have XP x86 SP3 and my cpu is C2D E6750.
By default, XP uses TSC(Timer Stamp Counter) working at 15ms.
I can see this using ClockRes by SysInternals or a program called TimerResolution.
Nexus Dock uses 1ms, but it seem to alter the whole system timer and XP gets set to 1ms also.
Why does this happen ? Is it forced by Windows or is Nexus altering the system ?
Is it possible to set the Dock to 1ms leaving the system at 15ms ?

The problem with the MM timer is that it is a 'global' timer, i.e.; used system wide - as such, when you change the timer resolution to 1ms, it affects the whole system.

I change the timer's resolution to 1 ms when needed via timeBeginPeriod and then change it back to default via timeEndPeriod when the operation that requires the 1 ms resolution has completed.

When you say "I change..." you mean you will alter the way Nexus handles the timer or it already works that way ?
Mine is set to 1ms always, doesn't return to 15ms.

Let's see, in practice there is no problem with the timer staying at 1 ms resolution instead of the default 15 ms. The only real difference is that the timer fires more often, but that does NOT mean system wide events happen 15 times faster - simply because they depend on a pre-set interval (e.g.; fire *every* 30 ms) and not on how often the timer fires (timer resolution).

So everything works as it should regardless of the current timer resolution.

Certain animations in Nexus require a 1 ms resolution in order to be smooth animations. If the timer resolution is much higher, those animations can become 'jerky' because Nexus can no longer accurately measure the time that passes between one frame of the animation and the other.

To recap: exiting Nexus should return the timer resolution to the default 15 ms, but, even if it doesn't, there is absolutely no problem. We are no longer running 8 Mhz CPU chips where a 1 ms timer resolution could have some weight on system performance.