I just installed the amd64 version of ubuntu 9.04 on my computer, and now need to install codeblocks to continue some software development. Unfortunately, I cannot find the right combination of steps to make this work.

I may need to install some wxwidgets packages to make this work, but when I tried to follow the instructions on how to add entries in sources.list, that did not work either.

Separately, I downloaded and installed ubuntu 9.04 from the DVD, which I would have thought had a great many packages included. However, I notice very few packages were installed, and relatively few packages seem to be listed in the package manager application when I select Applications + Add/Remove... (compared to what I recall having in ubuntu 8.04). Why is this?

Try looking in your Synaptic Package Manager you can find it under System--> Administration. Click reload to update the packages list, then type codeblock in the search field.