question about the Force

Do Jedi/Sith use the Force to seewhere their opponents lightsaber is going or are they just extremely aware of their opponent?

They're Jedi, they use the Force to see.

I think they explain it in ANH. The Force helps your body move, but you have to have the will to tell the Force what to do. Something like that.

It's a kind of attunement to the Force, knowing where the next swipe is coming from.

i once read a book where it says the Force tells and guides them where blasts go to deflect them. so im assuming its something like that.

Hmm...

When deflecting blaster shots, they can predict where the shots will hit; Jedi only deflect shots that will hit them or have a good chance of doing so.

When deflecting another lightsaber, though, usually the other combatant is a Force-user as well, and they nullify. The Force guides them in combat, but in lightsaber battles it really does come down to skill.

Either that, or they're just master swordsmen... Or any of the other possibilities that I don't give a shit about...

Pretty much...