From info in the first game (well the descriptions of various swords), i think the lightsabre came into use around 4000-5000 years before the OT.
Ajunta Pall did not have one, he lived 5000 years b4. But you have them in KotOR, which is 4000 years b4.
There was also the Karath swords, which belonged to a sect of the sith called the Karath (obviously but some1 who knows more about the EU could tell u more).
I don't know exactly. Does any else have any ideas?
I have decided to make a separate thread on this topic here.