Here's the NORMAL home network.
Broadband (cable, dsl, etc.) -> Router -> PCs.
You would never lose internet on any other machine in a normal setup. Did you have an abnormal setup?
OS win XP, I have a homenetwork and mine is the main computer which needs to be reformated, will I loose the broadband connection for the other 3 computers in the network doing this process my wireless set up is Netgear.