Your machine is called an "E P C" by the ePC community.
If running Linux, it has a modified version of Xandros on it.
Xandros is based on Debian, so uses Debian repositories. (Repositories are free software collections
typically accessible over the internet.)
Debian's utility for installing new software (and therefore Xandros' too) is through a program called
'apt'. On the ePC you can install, configure and use a GUI called 'synaptic' to download from repositories
containing software that is tested and works on the ePC and Xandros.
You should go to http://wiki.eeeuser.com/
for more info. eeeuser.com is a treasure trove of information
on your machine.
My advice is keep notes of everything you install, and how you installed it. (In case you want to restore
and start over.} Restoring to the "factory installed" OS is simple and quick (at last on my Eee PC 8G)
and is built into the machine.
Have fun. It's an amazing little machine.