I can connect to the internet, but not the host computer

[mpsmom]

I am on a wireless connection via a host computer in the same home. The other computer is connected to the qwest modem and a linksys router. I can connect to the internet, but not to the shared file on the other computer. We are in the same workgroup and I have tried just typing in the name of the other computer, but get an error msg that it can't be found. Can someone walk me through some troubleshooting. I tried going to the other machine and setting up a network with that computer as host and others connecting to the internet through it and got an error msg that other computers cannot connect to the internet through that machine (even though I already am).