Only an expert would be sure of listing all the registry entries. You could try searching for words such as auran, trainz, etc but that might not find them all.
John
It's just MRU's (most recently used list) and file association and uninstall info that's stored in the registry, none of which are needed to get it to work.
You don't actually have to reinstall assuming the Trainz folder exists say on a drive other than C or whatever is the system drive or you have saved it somewhere that isn't going to get wiped out by a reinstall of Windows.......
If you browse to trainz.exe and click on it, it will run, you can set up the shortcuts manually (right click on trainz.exe > send to > desktop) and also associate cdp's with CM2 if needed (right click on any cdp file > open with > browse to Auran/bin/ContentManager.exe and tick always open with).
MRU's and location will get added back into the registry the first time you launch Trainz, the uninstaller in the trainz folder should you need to, will work from there as it won't show up in add remove programs or the Vista / Win7 equivalent although if it was never installed to start with a simple delete achieves the same thing, looks like as with 99% of Windows programs it doesn't remove registry entries anyway. CCleaner however will do that job nicely.
For info......
You can actually copy Trainz from one PC to another or to another folder on the same PC where it is installed without actually installing it, just add the shortcut, call it say Trainz2 or Trainz backup. This method also works well if running Trainz in Linux with Wine.
You can also use a backup program to keep both versions in synch in case you mess one up or a patch doesn't work as expected, copying is a heck of a lot quicker than reinstall and re adding / committing Content
Also if, as I do you run multiboot systems you can have one copy of Trainz and use different OS's on the same PC.
For example I have Trainz installed on it's own drive and set up to run from XP, or Win7 with no problems and another set up to run with a couple of Linux OS's and XP.
Note that file association will only work for one copy per OS.
Malc