If you are using NAT meaning your IP address is 192.168.x.x or 10.x.x.x. and don't have any kinds of special firewalls installed people should be able to download from you without any problems. You haven't indicated why you feel you need to force your ip address.

I assume that the ip shown in whatsmyip.org is different from the one you see when you do an ipconfig. If you are not using a static ip address option with your isp then the IP you see on whatsmyip.org will in all likely-hood change if you reboot your equipment.

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Lee Evans, President
LeeWare Development
http://www.leeware.com