I use Virgin Media, but I'm not sure what you mean by 'password for the service'.

AFAIK you don't need a password to access the internet , just plug the cable modem in.

There is a password that you create which is used to call customer support, but AFAIK it's only used by the callcenter.

It's also worth noting that Virgin Media is nothing to do with virgin mobile, Virgin Media is still operated by the old telewest/NTL but they bought the Virgin branding.