local system time and /etc/localtime

Hi all.
Because I have dual-boot system (other OS is w2k),
local time is kept in system clock.
What is the right way to correctly set time zone in NetBSD
in such environment?
Setting /etc/localtime to /usr/share/zoneinfo/Europe/Minsk
gives +2 (or +3 hours),
sysctl -w kern.rtc_offset=-240
doesn't look good due to summer/winter time changes.

P.S.
Is this correct?
http://www.netbsd.org/guide/en/chap-boot.html
#chap-boot-system-time

-- 
Best regards, Aleksey Cheusov.