Language: English, software to view videos

To change to English, scroll to Settings on the Sansa and cpress the center button to choose it (it looks like an equalizer panel--I understand you are in Greek settings, so I will try to give you what the symbols look like).
Next, scroll to Language (in Greek the word "language" should look like this
γλώσσα) and select it, then choose English, and select it.
The software can be obtained from this page below. The downloads are on the right side of the page for your player.
http://www.sansa.com/support/sansa_e200/faqs