This section should now be of no relevance, since all versions of TTD that I know of are supported by TTDPatch. But if you're interested anyway, read on.
TTDPatch will have to know the locations of code that has to be patched. This will usually be a table that has to be compiled into the program to make it work.
If the version of TTD you are using is not known to TTDPatch, it will tell you so and offer the option to try and start anyway. However, this is a bit tricky, and may result in the program locking up, or causing a protection violation. Depending on your operating system, this may lead to complete hang of the computer. So, don't try this if you have any important programs running in the background.
These are the versions that are known to work: