<p>I'm on .NET 2.0, running under Medium Trust (so <a href="http://msdn.microsoft.com/en-us/library/system.timezoneinfo.aspx" rel="nofollow noreferrer">TimeZoneInfo</a> and the Registry are not allowed options).  I'm asking the user for two dates and a time zone, and would really love to be able to automatically determine whether I need to adjust the time zone for DST.  </p>

<p>This probably isn't even a valid scenario unless I have some <em>very</em> robust support, a la <a href="http://msdn.microsoft.com/en-us/library/system.timezoneinfo.aspx" rel="nofollow noreferrer">TimeZoneInfo</a>, to differentiate between all of the different varieties of Time Zones in the first place.</p>

Well, since
```
TimeZoneInfo
```
is excluded, you're probably not going to find a solution in the framework itself (but don't quote me on that).
In which case, have you considered reflectoring the
```
TimeZoneInfo
```
class and using what you find there?