You do have a modem there somewhere, don't you? Presuming it's a home network, you should have modem sitting between your adsl(phone line)/cable(fibre) and your new router. You would most likely have bought the e800 to provide some functionality your existing modem/router lacked, such as a switch (multiple lan ports) or wireless, or some sort of sophisticated packet management.
One potential conflict could be if your modem/router is serving up an address to the wan side of your e800 that is in the same address range as the e800 is using to serve up addresses on its lan side.
Ubuntu/linux is not really part of the problem, as long as its wireless hardware is working (which doesn't rely in any way on the e800). For example, your mobile phone should be able to connect to the wireless lan, without putting the e800 cd anywhere near it!
Try this: If you can connect your inspiron to the modem/router (the one the phone line/fibre cable is connected to) and get on the internet, then connect your computer to the e800 (without connecting anything else to the e800), go into the config (192.168.1.1) and turn off the dhcp server (will be under the lan settings somewhere). Then connect your modem/router to your e800, but to one of the e800's lan ports, rather than the wan (internet) port. Connect your inspiron to another of the lan ports, and you should be able to get on the internet. You will need to set up a password on the wifi, but it will function like a port on the lan switch. Good to go!
This is a simple way to avoid double nat without passing authentication from the modem/router to the e800 (disabling routing on the modem/router). The reason for disabling dhcp on the e800 is that dhcp is already provided by the modem/router. Not making use of routing on the e800 means that everything stays on the one lan address range, you're basically using it as a wired/wireless switch.