Device::SerialPort & ControlX10::CM17

Both modules are available via CPAN

perl -MCPAN -e 'install Device::SerialPort ControlX10::CM17'

after that, you should be to go.

Well, you also need a firecracker device. Look at http://www.x10.com, they're almost certainly having a sale somewhere that allows you to get a firecracker kit for only a few dollars. Make sure the e-mail address you use for your order confirmation is a junk mail address, though, 'cause they'll spam the heck out of the address you give them.