|I want to route an Ethernat Cable upstairs and connect to a Motorola Modem to boost my wireless signal upstairs.|
Plugging a modem in upstairs will do nothing. You need either a wireless Access Point (AP) or another wireless capable router. An AP would be simpler to configure and join to the network, but may very well be more expensive than a router.
If you go with a router, you'll definitely want to read my "How-to" guide that wanderer mentioned. Just click on my name above in this response and read my “how-to” guide titled, “Add a second router to your LAN”
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.