How to set time zone taking it from the user pc??
thats it:
one of my users is in mexico and he says calendar changes the day at 5:00pm at mexico. seems the calendar si set to India or something.

I believe you will need to use GMT time in conjunction with the time zone your user is in.
The calendar will display the time you set it to be. I usually do this at the server side.
If your user logs in, then you can use their setup information to collect their time zone.