timestamps and time zones

[2Hosts.com]

Bearing in mind the international nature of the internet, how do I make a
timestamp local to the user rather than local to my webserver in Canada?  If
a user is adding a record to my database from England, I want the timestamp
to be GMT rather than PST, and the same for my Australian clients, and so
on.

I will probably still use a "master" time stamp too which will be "master
server time" much like "ebay time".

How do I go about this?