Probably not the recomended method but when I built my latest PC using new drives I copied all the Trainz stuff to one of my other PC's, Installed Win7 then copied it all back, then manually set up the shortcuts. Not had any problems and avoids going through the patching saga again.
Mine
If you are keeping the drives and Trainz isn't on the system drive you can just add the drive and set up the shortcuts. Registry entries are created after the first run.
Alternatively just install and the copy the original over the top, again saves patching but you get the shortcuts and registry entries without any need to fiddle.