lme vs lme4

Hello,

We are attempting to compare some results using lme and lme4.  I'm 
relatively new to this so could well be asking questions that are overly 
simplistic or naive, if so please inform.

We have an example that works with nlme(lme) and specifying the weights 
as the function varConstPower, however when we try to do a slightly more 
specific analysis using lme4(lmer) it doesn't seem to have the 
varConstPower function built it.  Is in nonsensical to build it into 
lme4?  It might well have some shortcomings/compromises. Is there a way 
we could accomplish the same thing with lme4 via some R coding or any 
other method?

All suggestions most welcome.

Thanks

Jim

Jim Maas
University of East Anglia