Got a mate I'll have to look at her setup in the weekend.

Basicly they have Telstra Cable with a Motorola SB5101 modem and this works fine with direct ethernet connection to pc.
The want to share the connection with 2 pcs with a Linksys WRT54G but apparently this is not working via cable modem to "internet" port on linksys router then ethernet to PC? Once this is working then wireless to another pc.

Any ideas where I should start in the weekend? (I have never worked with cable only adsl)