IP addresses up to 223.255.255.255 are used for normal routed IP networking, from 224.0.0.0 they are special. You will find addresses 224.0.0.X often occurring on networks with large routers, as these are group addresses used to locate types of machines (e.g. any router). Unless you are using complex inter-router protocols, you can disregard (and drop) such packets in your configuration. The address 255.255.255.255 is a special address which means a local network broadcast. It is received by all machines on your subnet and is not routed to your ISP or other subnets.
It is worth noting that 127.X.X.X is also special in that it is normally directed to a local loop back interface. 127.0.0.1 is an address for yourself (also called localhost) from most computers.