click here for USB Q&A. For a USB connection the two PCs would have to be quite close together so this could be quite limiting. However, since both PCs can't use the same phone line to connect to the Internet at the same time it may be better to remove the modem from the older PC and replace it with a network card. With both PCs networked by ethernet you could then use Internet Connection Sharing via the newer PC. You could also share a printer over a proper network.