On linux you can have multiple IPs per physical device. You can create a virtual Ethernet interface on eth0 with ifconfig eth0:1 10.1.1.1 netmask 255.255.255.0, for example. You can sometimes set the hardware address with ifconfig, too, but it depends on whether or not your driver allows the SIOCSIFHWADDR ioctl. Or you can use the ioctl in perl like this (untested):

require "ioctl.ph";
use Fcntl;
...
sysopen ETHER, "/dev/your-ethernet-device", O_RDONLY;
# You'll need to pack the address into $addr.
ioctl ETHER, &SIOCSIFHWADDR, $addr;
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You might check out libnet which is a tool for building packets. You could probably build the xs files. The libnet on CPAN is not the same thing. You could also try some hacker sites as they use such techniques for attacking systems...

W2k lets you set multiple IP addresses on an interface, too, but I don't know how to refer to them in a program. HTH, --traveler