install problem on FC5

[PortMan]

I had a problem installing ISPConfig on FC5:
I have my server using a private IP of 192.168.1.10 behind my Netopia router. The public IP to access the server is 75.10.1.220 and I have added an IPMap to the box. I had used the "Perfect FC5 Install" guide and everything works. I can get to the website (default install of Apache), SSH, dns, etc of the server. The problem comes when trying to install ISPConfig and get to the part where I specify:

Please enter your MySQL server: localhost
Please enter your MySQL user: root
Please enter your MySQL password: MySQL password
Please enter a name for the ISPConfig database: ispconfigdb
Please enter the IP address of the ISPConfig web: 192.168.0.10
Please enter the host name: www
Please enter the domain: mydomain.com

Everything works until the "Please enter the domain: mydomain.com"
I put in the domain.com and it won't take it. It erros with "The URL is not reachable". How do I correct this?