This doesn't get your IP address but does solve your underlying problem:
Install Apple Bonjour for Windows on the machines you use, and you can reach the websites on them as http://[machinename].local/. Apple Bonjour uses the ZeroConf networking standards to resolve hosts in the .local domain without any kind of central server. It's built in to Mac OS, and there is a linux implementation included in most distros called Avahi.
It even works over the 169.254.x.x link local IP addresses you get that usually mean your computer has failed to get an IP address with just a crossover cable between two machines.
I use it to allow windows-equipped colleagues to access test web sites hosted on my MacBook.