avivai,

One might hear "proto-Hebrew" and assume that Hebrew and proto-Hebrew are two different languages. However, the use of terms like "Proto-" or "Paleo-Hebrew" (the script is called K'tav Ivri in Hebrew) denote a style of script rather than a different language. In the case of all of the scripts the names of the letters, the order, and numerical values of the letters are the same.

Just as today we have the Ashuri script, Rashi script, and cursive, there are also closely related scripts which can be found on historical pieces such as the Gezer calendar (Israel between the time of the last judges and the time of David), the Tel Dan (by Aramean king) and Mesha (by Moabite king) steles, the Siloam (in Judah during the reign of Hezekiah) inscription, in seals in and around Israel and Judah throughout the First Temple period, as well as coins stretching even through to the close of the Second Temple period (including during the Bar Kochba Revolt).

There is at least one instance in the Dead Sea Scrolls in the Habakkuk commentary (and I think in a Psalm) where the scrolls are written entirely in the Ashuri script, except for Hashem, which is set apart and written in proto- or paleo-Hebrew. I believe there are a small handful of opinions regarding whether the Torah was originally given in K'tav Ivri or K'tav Ashuri. Perhaps someone else can elaborate on the opinions on the scripts.

Here is a link: http://www.mezuzah.net/scripts.html