"To me this proved conclusively thet the internet connection was waking the pc fron stanby ."
While the detail in your post is lacking my only guess is that in your BIOS you need to disable WOL or Wake On Lan.
I have carried out a comprhensive test on my pc to try to establish the cause of the pc coming out of standby .
I disconnected all peripherals as the start point because I can see if the machine is on or not , then connected each one to see if it affected the problem the last check was with and then without the cable modem connection (ethernet) . To me this proved conclusively thet the internet connection was waking the pc fron stanby . I hae tried to uninstall the cable package (NTLI is the ISP and the modem is Agere )but the uninstall will not perform . I am now into uncharted waters , any advice ?