1) Program Files (x86) is the folder for 32-bit applications to be installed to 64-bit machines. Sins will run just fine from that directory.
2) Sins works fine on 64-bit Vista (I know this from personal experience). You should be fine using Win7 64-bit to play Sins.
In fact, using 64-bit to run Sins can be even better than 32-bit, as 64-bit will utilize more RAM than 32-bit; this is especially useful as Sins caches almost everything using the RAM.
Also, in order for it to work properly (this is on Vista and presumably Win7)- ONLY INSTALL SINS FOR THE CURRENT USER!!!! This is important as if you install for ALL users then it will not work.
Other than that, you should be able to run it fine.
