The only drawbacks are that your computer is out in the open, and has to be left on whenever someone else on your network wants to go online.
Get a ethernet hub. Any hub will do, all you need is 2 ports and an uplink.
Plug your cable modem into the Uplink port on the hub. Plug your main computer into port 1 on the hub, and the uplink port on the router into port 2 on the hub.
Configure the main computer to connect to the internet normally.
For Windows 2000 (Possibly ME and/or XP):
Go into the Control Panel, and then "Network and Dialup Connections". Right click the connection which you use, and click Sharing. Enable sharing for the connection.
For Windows 98 (Possibly ME and/or XP):
Download, install, and configure one of the many internet connection sharing programs available on the internet. Many are freeware, but the shareware programs are more reliable.
Plug all of the other computers on your network into the router.
Configure the router as follows: