So I have 3 home routers, 1 belkin and 2 netgear. I have my ISP internet connection coming into my belkin, which I then have the 2 netgear routers (from their WAN) plugged into Belkins LAN ports. Now the Ubuntu computers I have on Netgear LAN 1 and Netgear LAN2 can get to Belkin just fine (at 192.168.1.1), but I am unable to access a computer on LAN1 from a computer on LAN2 and vice-versa. My Belkin is 192.168.1.1, my Netgear1 WAN is 192.168.1.100 and Netgear2 WAN is 192.168.1.200. I have the netgears both assigning DHCP IP's from range of 192.168.0.100 to 192.168.0.150 on their LAN ports.

Now, I have set Netgear LAN1 port 80 NAT'd to go to one of my computers on it. I try to access 192.168.1.100:80 from a computer on Netgear LAN2 network and it say host unreachable.

What am I doing wrong?

You're double-NATing (triple?). Why would you do that? Go ISP -> Belkin -> Switch(es) -> Computers; note switches instead of routers. If you don't have any real switches, see if your Netgears have an option to just act as a switch. It will make everything a lot easier.