[R] contrasts for lm

[Ann Hess]

I would like estimate a number of contrasts from a one-way ANOVA model.  I see 
that the lm command has a contrasts option, but I can't figure out how to use 
it!  Any help that can be offered would be greatly apreciated.

Here is my model statement:

Model<-lm(log2PM~P+T+P*T)

where P has 16 levels, T(treatment) has 12 levels and I am interested in 
looking at different treatment comparisons.

Thanks!

Ann