  The in-plane ($\rho_{ab}$) and c-axis ($\rho_c$) resistivities, and the
magnetoresistivity of single crystals $Na_xCoO_2$ with x = 0.7, 0.5 and 0.3
were studied systematically. $\rho_{ab}(T)$ shows similar temperature
dependence between $Na_{0.3}CoO_2$ and $Na_{0.7}CoO_2$, while $\rho_c(T)$ is
quite different. A dimensional crossover from two to three occurs with
decreasing Na concentration from 0.7 to 0.3. The angular dependence of in-plane
magnetoresistivity for 0.5 sample shows a \emph{"d-wave-like"} symmetry at 2K,
while the \emph{"p-wave-like"} symmetry at 20 K. These results give an evidence
for existence of a \emph{spin ordering orientation} below 20 K turned by
external field, like the stripes in cuprates.
