It appears that Asus has seen fit to supply 2Gs without working e-mail clients. Thunderbird also does not appear in the default repositories for the 2G which contain the number 700, rather than the repositories for the 4G which contain the number 701. The first step in this article deals with the editing of these repositories in the sources.list file. Before doing this it would be worth reading the wiki article Adding Additional Software Repositories
This article is derived from information garnered over a number of threads in the forum but summarised in this one.
sudo nano /etc/apt/sources.list
making the modifcation, then saving (Ctrl+o, Enter), then exiting (Ctrl+x)
sudo apt-get update
NOTE: If you get an error message, try the next steps anyway. The error message may not be material.
sudo apt-get install thunderbird
sudo apt-get install eeepc-updatepack-20071126
Alternatively, install Thunderbird and the Update Pack via Synaptic.
If you want to add icons/shortcuts to Easy Mode, download the Thunderbird icons from Alternative Icons for Common Applications and learn how to install them from Adding icons to Easy Mode on this wiki.
The thread in which this was summarised was mainly contributed to by Neil and Niel1952 but it depended on information provided by sliverstorm, Wilden, TheWalt and others in other threads.