|The stupid question is the question not asked
As has been discussed here many times before, blocking on IP will not work. Every AOL, dial-up and many NAT users will be allocated a different IP each time they connect.
Alternatively, where many users inside a LAN get to the internet through a common firewall, NAT or proxy, one IP will translate to many users. Without using some sort of cookie system, you will have considerable trouble determining which users have voted for what.