Its all still working perfectly, so far.
Homegroup is set up and file sharing and printing from other pc is working.
I think I'll back up the router settings just in case it gets reset by accident or something.
Thanks for everyone's help.
Lets say for example you have an ADSL router setup as follows
Internet Facing IP <== MODEM ==> 192.168.1.0
The Modem will have an IP address which is seen by the Internet, and anyone on the Internet can see that IP address. The LAN port is then connected to your private network, the 192.168.1.0 network. The internet peoplez cant see this network, as it exists only in your premises. The Modem then acts as a gateway device using NAT etc to give everyone on your local network access to the Internet. Theoretically, if not configured correctly, then outside people can access your internal network, but this would require you to set up very dodgy port forwarding. (Not that port-forwarding is dodgy, just misconfigured port forwarding). But Basically your router acts as a gateway between two logically separated networks. The WAN port connects to the one (Internet side) and the 4 LAN ports to your local one.
The WAN port on your WIFI router would normally plug into the LAN port of your ADSL router, allowing you to create a logically separated network from the ADSL network. This might be useful in some circumstances, but in your case it was not. You wanted your WIFI and ADSL LAN to all be in the 192.168.100.0 network, so we plugged into the LAN Ports.
If for example you want a network whereby all your Wireless devices have access to all devices on the network, but devices not on the wireless network cannot see the wireless devices, then you would plug the ADSL LAN port to the WIFI Router WAN port, and create a logically separated network for the Wireless guys
Internet IP <== MODEM ==> 192.168.100.0 <== WIFI router ==> 192.168.101.0
Like the modem allows people on the 192.168.100.0 network to see the Internet, but stops the people on the Internet being able to see your 192.168.100.0 network, the WIFI router allows the people on the 192.168.101.0 network to see the 192.168.100.0 (and thus the Internet), but the 192.168.100.0 network cannot see the 192.168.101.0 network.
This only occurs when you use the WAN port.
By using the LAN ports, you are all part of the same logical network, therefore no routing required. Hence the fact that your setup now works the way you want it.
Hope this explains it well enough.
I don't say much, but if I do say something, it pays to listen.
Yes, thank you.
I know a heck of a lot more now than I did a couple of days ago.
Thanks for all your help.
Haha, whenever I don't use wifi, I normally just switch off the router to keep other people from hacking it or stealing internet.
But now I can't anymore as my main PC don't have internet as well.
Not a big problem, i'll just beef up my wifi security and check more often who is using it.