Hi Graza,
UTC is the new name for GMT. You don't need UTC if your hardware clock is not specially UTC.
CEST is Central European Summer Time and means that you have Daylight Saving Time enabled. Sunday, it will become CET (if you have the rigkt package tzdata).
The dates of change are automatically set in /etc/localtime which is a copy of /usr/share/zoneinfo/"your_contry".
Then, for a change this week-end you might have the rpm "tzdata-2006......" installed, check it with command "rpm -q tzdata".
Patrick