Here's how to do it for free:
Using the tzedit.exe tool from Microsoft:
Download the tzedit.exe tool using the link under Windows 2000 from the Preparing for daylight saving time changes in 2007 Microsoft web page.
Unzip the files into a Windows program directory such as c:\Program Files\TZEdit
Apply the tzedit.exe process to your systems:
1. Exit out of applications.
2. Run the executable tzedit.exe using Start > Run, provide the full path, for example: c:\Program Files\TZEdit\tzedit.exe
3. Your current time zone should be highlighted. Click the Edit button.
4. Set Start Day to Second Sunday, March.
5. Set Last Day to First Sunday, November.
6. Click OK.
7. Click Close.
You need to change your time zone twice using the Windows Date and Time Control Panel applet.
1. From the Start menu, click Settings > Control Panel and then click Date and Time.
2. Click the Time Zone tab.
3. Select a different time zone and click Apply.
4. Now, select your time zone and click Apply, then click OK.
5. Restart your applications.
Probably best to do this in Safe Mode, but hey, whatever works. I just made sure Firefox and any auto-updating software was closed first. Works a treat. You can even create your own time-zones using this tool, but that isn't so advisable ;)