If you have only two machines and you are not going to add more then there is little benifit in a hub or a switch. If you want to share your BB connection and you want to access the internet on the machine upstairs without the other machine being on then you will need a router.
The difference between a hub and a switch is as follows...
A hub uses a global broadcast to communicate with the devices attached. If one device wants to talk to another it will send a message to every port on the hub until the correct device responds.
A switch is more intelligent. The switch will learn what devices are attached. When a device want to send a message to another, the switch will only send it to the port with the recipient deivce on. This means network traffic will be reduced!
The price difference is next to nothing, so a switch will always be the better buy.