Why don't you play around with GNS3 already installed on Ubuntu in a VM - you can download my install from http://rednectar.net/gns3-workbench
. I'm also just finishing off a series of three articles that talks about linking GNS3 topologies to your external network - you'll find the first two of these at the same site (http://rednectar.net
) - just look under the "Recent Posts" on the right.
Now I understand that you probably don't want to do the VM thing, just want to put it straight onto a raw Linux box, but in the VM you'll find a diary af everything I did to get it working in Ubuntu - if you'd just like a copy of that log/diary, and skip the whole VM thing, let me know & I'll dig it out.
-a VMware image of Ubuntu with GNS3 and VPCS installed and a collection of exercises/labs