dnatting

[Payal Rathod <payal-netfilter@scriptkitchen.com>]

Hi,
I have a rule on my friend's broadband connection to redirect traffic 
from outside to an internal machine like,

iptables -A PREROUTING -d 1.2.3.4 -p tcp -m tcp --dport 80 -j DNAT  \
--to-destination 192.168.10.10:80

But she complained that people from inside the network cannot do
http://1.2.3.4 in their browser and see the site. Is she correct?
What is wrong with my rule because I can see the site from outside?

Thanks in advance.
With warm regards,
-Payal