There are hundreds if not thousands of users running Trainz Win7 that are not having the problems either Erik or Anna are having. I installed it on Win7 Pro 64 for a while to do some testing with no issues, although I much prefer Win XP. Thus, I suspect something maybe wrong with your settings.
That said, reinstalling to a separate location other than Program Files is probably a good idea. However, you do not need to delete the existing installation if you have content you want to keep. Just install it, patch to the level of your existing installation, and copy the old installation over top of the new. For that matter, you can just copy your existing installation anywhere you please and run it from there, although you would manually need to set up protocol handlers to process CDP files and, perhaps, the Trainz download cart, if you use the things.