Fortunately for you, there are some kindhearted third-party developers out there who have developed free DST patches for the following operating systems. Naturally, Microsoft and Apple won't support these fixes (nor can I), so use these at your own risk.
Unofficial DST
Read about IntelliAdmin's free patch
Download the NT/2000 patch now
Unofficial DST
Read about IntelliAdmin's free patch
Download the 98/Me patch now
Unofficial DST 2007 Patch for Mac OS X 10.0 through 10.2.8 (Jaguar)
Read about the University of New Hampshire's free patch
Download the 10.0-10.2.8 patch now
( Mirror: http://macfiles.brothersoft.com/utilities/system/DST_Update.mpkg.zip )
Unofficial DST 2007 Patch for Mac OS 8.5 through Mac OS 9.2.2
Read about Glenn Anderson's free patch
Download the 8.5-9.2.2 patch now (please read the above article first for important notes, and see here to learn when DST changes in the U.S. now)
Read about an alternate fix suggested by Marcel Brown here
What about Windows 95?
According to Steve Wiseman from IntelliAdmin (the guy who made the 98/Me patch above), "Daylight saving time is simply broken in Windows 95, so I wouldn't even bother trying to apply the patch to these systems." If you want to try to manually patch it, there are instructions available on the Web, for example here or here. You can also try keeping your time in synch with a freeware/donationware (free and donation-supported for home and education use; $10 required for commercial use) utility called Dimension 4.
What about [insert some other OS here]?
Windows Vista has native support for the 2007 DST changes.
Windows XP SP2 has a patch available through Windows Update or from here (if using XP SP1 or XP without a service pack, upgrade via Windows Update first).
For more information from Microsoft on how the DST change affects its software, please see this page.
Mac OS X 10.4.6 (Tiger) has native support for DST 2007 (if using 10.4.5 or below, upgrade via Software Update; if using 10.4.6 or later, no patch is required).
Mac OS X 10.3.9 (Panther) has a patch available through Software Update or from here (if using 10.3.8 or below, upgrade to 10.3.9 via Software Update first).
For more information from Apple on how the DST change affects its software, please see this article.
For any other OS or product, check with the manufacturer or Google it.
*Please note that Daylight Saving Time shouldn't be your only concern when running an OS that's no longer supported. System security is also a potentially serious problem after the manufacturer stops releasing security-related updates for the product, and chances are that many developers of third-party software will have stopped releasing updates that are compatible with your OS as well. This can potentially leave your system vulnerable to a multitude of attacks. From a security standpoint, it's always best to use a system running a currently-supported OS and keeping it patched rather than continuing to use legacy systems.
If you found this information useful, please consider making a donation of any amount. Even $2 or $3 would be awesome! Thanks!
UPDATE, 31 Oct 2011: A reader notified me that the links for the Mac OS X utility were no longer working. Thankfully, the Internet Archive Wayback Machine has copies of both the utility and its homepage, so I've updated the links. I also included the address for another site offering the file, updated other links, gave a link to Dimension 4 for Windows 95 users, and made a few other tweaks.
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