Very Newby - help needed please

Hi,
I am very new to Ubuntu and EMC2. I have just installed Ubuntu 10.4 from the CD release. I am trying to update the EMC packages and found that I cannot connect to any site via update manager or Firefox. I followed the trouble shooter help and could ping any address on the web. I can also use the Network tools to look at anything. I just cannot to the internet with any software.
I am going through a wireless router for the 3G connection.

I hope this is the right place to ask but if not please point me in the right direction.

check the MTU value in the wireless connection setup in ubuntu , and reduce the value to say 1200 , then if it works and everything updated then change it back to 1500 which i think is default
this could of course be a problem with your router or 3G connection settings . updating a large amount of data over 3G can be problematic with disconnections .

and depending on the 3G provider some sites are cached
and could be a firewall issue

i would suggest setting up , and updating from a wired connection first .

Thanks for the reply. I did as you suggested with no change in the situation.

The 3G router is an existing network with two or three other computers using the internet connection already. I can see the internet with ping or Whois but I dont have a connection to the internet.
In summary, the 3G works, even for Ubuntu but I cannot connect via HTTP.

I can also use the Network tools to look at anything.

From Network Tools - when you run NetStat on Routing Table Info, which interfaces do you see, with which gateway addresses?

Same sort of thing, if you run /etc/init.d/networking restart what interface does it say it has connected to?

I followed the trouble shooter help and could ping any address on the web

ping uses icmp not tcp so not testing the same thing.

Going to need to know a whole lot more about the router model, how it is connected precisely to help any further.

Sure it is not something as simple as the router not having been specifically set to allow UDP/TCP traffic to the LAN address allocated to your new computer?
Some routers use an address range for access in the firewall rules.

regards