How can I play the original Touhou games?
Well you can either buy it on steam (the games are hidden for some reason, but you can find them here). However do note that the earlier games (6-9) weren't released on steam. If you want to play those games, you can hunt for the original cd's, which is not recommended in my opinion.
Another way of obtaining the games is by pirating!!! You can download all the games at moriyashrine.org. The best thing is, that the games already ship with an unofficial english patch, and the older games also work on modern computers out of the box.