Lets see what we can do....
First of all don't worry, money hasn't been wasted as these cards are just like a network card nothing to do with broadband.
How have you setup your network? Does the router plug in to your PC and connect wirelessly to the PC's upstairs or are they all connected wirelessly?
Can all the computers seeone another on the network neighbourhood? If so good, we can make a start. If not make sure they are all in the same "workgroup".
In order to share a printer it has to be set as a shared resource, usually by right clicking on the printer and choose "sharing" and allow it to be shared. Once done a little hand icon should appear under the printer icon. To use the printer on the other computers just install as for a normal printer but remember to pick the Networked printer option.
For sharing dial up you will need to make your computer the gateway. If you have windows XP right click on the connection you use (in the network connections window) and choose properties. The last tab on the right marked "Advanced" has all the bits you need and is fairly straight forward.
Hope this is of use and please ask if you have any more questions.