Welcome, Tim! There are two belts for the drive, one for eng. to intermediate drive sheave, one from there to the tranny. In addition to the service manual, get registered with JDParts online. You will find that in many cases a question can be answered just by looking at the parts diagrams.
No so with your question now, however. If you have a good dealer near you, they may have a picture of the belt routing that they can print off for you. They have access to things we can't get to thru JDParts.
For some reason, I have no photos of the front (engine) belt. Only thing I have is this one showing the rear belt and springs. What is unusual is the belt runs on the "V" side of a flat idler (shown) and on the other flat idler it is on the flat side of the belt, which is normal.
If you or a friend has a 70 lawn tractor you could take a look at it. The belt routing is very nearly the same, maybe identical.
Get new belts from Deere to avoid a lot of problems if replacements are needed.
Have fun with the 100.