That would probably depend on the modem, but I wouldn't do that anyway.
What I would do:
1) Get a wireless G router that has a 4-port ethernet switch (not a B router and none of the super G etc stuff). 2) Connect the PC to the switch using ethernet (drop the USB crap). If you don't have an ethernet card on the PC they're only $10-20 or you could also go wireless if you don't want to have the router near the PC for $20-40. 3) Get a wireless card for the laptop if it doesn't already have one. Same brand as router if possible. 4) The brand should be Netgear or Linksys (my preference) and the router should be avail. for $30 for Netgear and $40 for Linksys on sale almost every week at one store or another. 5) Follow instructions with router for setup.