You don't need to worry about the difference between the server and the client with regards to DST.
It is always an offset based on what the current date/time is on the users machine.
The registry settings and the fact that rules change for DST are all moot if the offset is calculated at runtime.
Example:
User A from Pluto makes a post in the forums and the server is on Mars using MLT (Mars Local Time).
The server on Mars stores the post in it's system after first converting it's local time to UGT (Universal Galactic Time).
User B from Earth comes along and wants to read the latest post by User A.
When User B requests the page, their browser sends an offset (calculated from their current local time in relation to UGT).
The Server then takes this offset and applies it to the date/time it had stored for the initial post so it can return that information to User B relative to their current local time.
Now, let's say that same User A wanted to come back 10 years later and Pluto had adopted a new time system because a new planet had been dicovered next door to them that had really cool clocks.
User A would send their new offset from UGT to the server, and the server could show them when their old post was made in relation to their new way of keeping track of time.
In other words, it's all relative. If you fix the point of reference, then all other points can be expressed relative to that fixed point.