your own system? If you are talking about sites, then, yes. but you have remove any adsense ads if present while applying for adsense.
so, u mean u can't create a multiple accounts (not a single person, my friends new account creation )in one IP Address???
thats not true. one friend can refer another and thats where adsense referral program came into play at the begining. same IP is not a problem, as long as the accounts are not created for the same person thats fine. cyber cafe's have one IP all year long, how many people you think sign up for adsense from there all the time? so the answer is, sure you can.