[R-sig-ME] Help with analyzing multivariate outcomes

[marKo]

I have some problems analyzing multivariate dependent variables using a 
mixed-effect approach.
My dataset consists of two-dimensional outcome (like a position on a 
grid) measured approx 300 times for 100 subjects.
For one dimension the model would be something like that:

m1<-lmer(y1~time+(time|id),...)

but I would like to analyze the y2 as well (not in an independent 
analysis). I do not wont to decompose the data (PCA or similar) and than 
conduct the analysis on on the first component (i guess that it would 
not be appropriate). I somehow want to model the trajectories (basic 
idea). I know that the problem is not so well explained and fuzzy (it is 
like this in my head to)

Any ideas, suggestions, readings would be greatly appreciated.

Thanks a lot,

Marko