Alot of stuff that I've found in the hill country have been called "knives." (Or at least that's what I've been told) When I show them to people that don't know anything about artifacts they say "nice spearpoint!) I've never been on a dig and heard anything called a spear point... What is the difference between the two?
The only thing I can think of is the age of the point and the purpose for it at that time in history.. Can anyone help me out?

Well, in the first place, you already know more about artifacts than those referring to them as spear points! Actually, there is some merrit to the term in the sense that alot of these nice big points..like big perds,nolans,castroville,marshall,montell,etc.,and especially many of the large long auriculate and lancolate points were far to heavy to have been shot like an arrow or bird point. Instead, they were hafted to long wooden poles and atlatles and used like spears primarily for bring down larger game, and critters that could hurt them if they got too close. Knives were also hafted to wooden handles, but used as hand held knives instead of being hurled through the air at something.

Spears have long shafts and knives have short handles....... like some people. Actually, wear marks or lack of same on the edges of the piece will show up under high magnification and may indicate usage patterns. Generally long pieces were knife blades rather than spearheads. An exception would be long spearheads on lances specifically used for war or ceremonies. A long heavy head on a dartpoint used in conjunction with an atlatl could be detrimental to the overall balance of the unit. Early man in American did hunt mammoths and other megafauna and may have used thrusting spears with large spearheads in the harvest of such. Our ignorance of the activities of Paleoamericans is balanced somewhat by our enthusiasm.

in response to redman's last comment: ain't that the truth

Yes, not only factually put, but most eloquent to boot!