First, give yourself a static ip address on your network. Forward port 80 and 21 to your ip address (this is for web and ftp). Set-up a dynamic ip account on a site such as dyndns.org or no-ip.com. Then put one of the ip update clients on your mac so it will keep your ip address updated.
After this is set-up, pull up your web address in a web browser and you will make it to your mac. FTP is the same way just type in the address. I use this all the time and it works as well as can be expected.