If you mean alkalines, yes. My 4D P7 uses a linear regulator, and drops out of regulation (effectively into direct drive) after only about 5 minutes. But if you want the option of running from any of KOH, NiMH, or NiCd, you'll need some sort of regulation. (Well, a resistor would work, but it would hurt the already poor performance of KOH batteries.)
An 8xAMC7135 driver works quite well for this, as long as it's properly heatsinked.
Kaidomain has a 2.8A driver that is reported to be 8xAMC7135, but I just picked up a 10-pack of 1.4A (4xAMC7135) boards from DX and soldered 2 of them back-to-back.
Not sure why you want to use a resistor, but the resistance needed varies with the Vf of your particular P7, the internal resistance of your AAs, the resistance of the Mag, and the resistance of your battery carrier(s). Somewhere around a quarter of an ohm, and at least 2 watts, would be a sane starting point if you can't determine the approximate characteristics and calculate the right value.
If it were me I would definitely stay away from alkalines. They can't power a P7 at full power and have any decent amount of runtime. I would invest in some good batteries. Alkalines are also prone to leaking.
