[R] Mixed effects model

[Law, Jacqueline {Regu~Pleasanton}]

Dear all,

I am having troubles specifying the formula in the function aov. The model that I want to estimate is
   Y(i,j) = a + b*X1(i) + c*X2(j) + d*X1(i)*X2(j) + e(i,j)
where X1 is a factor variable, fixed
X2 is a factor variable, fixed
the interaction term X1*X2 is random

I would like to get the estimates for the fixed effects X1 and X2. 

Thanks very much for your help!

- Jacqueline