I heard a rumour that it was possible to construct a vorpal sword in BGI? Can anyone confirm this? Thanks

Nope. Only in BG2.

I know it is possible in BGII but I never heard that it exists in BGI and I never saw it on any list of swords you can create using CLUA, so I think its propably just a rumor.

What the heck is a Vorpal Sword? Like what is it's specs?

There is a vampiric sword, vorpal is in BG2 i remember that now. For the Vampric sword you need the Ancient Armor from the Firewine ruins and something else that i forget. Oh, yeah the idol of kozah from the archeolgical dig. IIRC you have to take them to Ulcaster's ghost.

A Vampiric Sword? Is that the sword that does damage to the wielder instead of the attacked creature?

BTW that is the only point to the Ulcaster school and the firewine ruins besides exp.

Yeah, what exactly does the vampiric sword do?

Properties: CURSED
Does the same damage (I think) as a normal Long Sword--to the wielder. Heals the victim by the same amount. I forget if there's a THAC0 bonus/strikes as magical weapon.
Not usable by:
Mage
Cleric
Druid
the Lucky Ones

Once (and only once) I made the effort to get this sword, just so I could say I'd done it. The only thing worth doing with it was to give it to someone like Kegain, who has 20 constitution. He used it to hit the other party members until they were healed and he was hurt. Then we slept, or travelled, so that Kegain could regenerate his HP. BUT it was such a lot of effort, especially because the sword is cursed and needed a spell to de-equip it.

To mis-quote the old Sword Coast proverb - "A Dwarf needs this sword like a fish needs a bicycle."