For theoretical (mathematical) kinetics, not too terribly difficult if you have the proper mathematics background:
"Proper Mathematics Background":
Calculus through optimization
Matrix algebra
Ordinary and Partial Differential Equations
Numerical Methods (Chebyshev's, Kolmogorov, and Runge-Kutta algorithms)
For applied (experiemental) kinetics, you need a solid background in statistics (multivariate at the Neter, et. al, Applied Linear Regression Models level, semiparametric methods like Poisson and Cox PH), programming in S-Plus or R, and the willingness to let Ralph the rat die for advancing science.
VERY, VERY few people show up to that graduate program with that background. That's okay, but you may have to do a preliminary mathematics year to catch up. It can be done at the pharmacy level. At UMN, we have a 4th year student in that preparation right now.