Re: weaponry in the movie
The prequel book has them going up against T-600s, T-1s, and HKs, not T-800s (the Arnold model). The current weaponry will take them out, but it's tough, and they often used large explosives or aircraft weaponry to take them out. These things weren't readily available to Kyle Reese in 1984, but they would have been available to the military.
Regarding the book: They did mention that most small-arms fire is virtually useless against Terminators (even the non-T-800s that they're up against). You need something with decent penetration.