I would do the following ..
Each computer requires a ethernet adapter .....(either wired or wireless )
1- 4 port router ........ and again either wired or wireless

Then the connection is simple ...... incoming internet connection goes into the broadband modem ......
From the output of the modem to the imput of the router .
From the output of the 4 port router to each of the 3 computers via their ethernet adapter ( using a CAT 5 cable or wireless if the router and ethernet adapters are wireless )
It doesnt matter which operating system is installed on the various pcs .......they are all now connected to the net .
I think this is what your trying to do.