There is a simple little utility, tzedit.exe, available from Microsoft, that allows you to change the DST start/end dates:
Scroll way down to near the bottom of that page (or select from On This Page) to "Method 2: Change the time zone settings on a single computer". Specified for XP/2000. Don't know if it works in 98 or
98ME:Dick Ballard snipped-for-privacy@att.net