Do you have an ISP (Internet Service Provider)? Dial-up or broadband? If it's dial-up, you should probably give them a call and see if they support Macs, some don't. If it's broadband, your DSL or cable modem probably has an ethernet port. Plug your iMac into the ethernet port, and it will just work. (You may have to reset the modem if it's cable because of DNS issues that crop up when switching connected device.)