small stepper driver

i need some help........i have just bought 3 Vexta 305 oz-in 2 phase
steppers@4.5A 2 phase excitation,2Vdc. and am trying to determine
what kind of driver i can get that is not too expensive(ie.gecko's)
xylotex.com has a 3axis ,2.5A bipolar driver . my question is can i
use this driver to run these motors with a 24Vdc/12A power supply if
i run them in series?if so , do i need to use some kind of resister
for current limiting? and what (approx.)i know that running steppers
in parallel is better, but i cant use this driver if i run them so.
what would the torque then be with these motors in series in this
setup with the xylotex driver?
i ve also been looking at an up to 15A, 3 axis unipolar driver from
stepperworld.com that would definately have no problems running my
motors, but i read that using a unipolar driver is a bad idea
considering the lower performance of it compared to bipolar drivers.
is this true??what would the actual performance(estimated)be if i
used this stepperworld driver compared to the other xylotex driver?

i want the best performance i can get without spending more than the
whole grizzly minimill cost to begin with. which direction should i
go?? ive asked the same questions in the mini mill group but i have
yet to recieve a clear and concise answer or suggestion(not that i
can understand anyway
any help would be great..thanks