[CentOS] DHCPd Config

I've read a number of articles, googled the web for a few months and
now attempting at turning my CentOS box into a gateway for the third
time. Configured my dhcpd.conf and other related files and all seems
to be working, I can have my M$ desktop leasing an ip address and all.

The problem is when I want to go out to the internet I keep on getting
the Request Timed out error.

I'm pretty sure I've followed the manuals to the letter. The hardware
is working fine.

Any clues or pointers would be very much appreciated.

TIA,
Joao