R help - Mar 2005 - lme user-defined correlation structures??

Could somebody help with the definition of new correlation structure for use
with a linear mixed-effects model (package nlme). Specifically, I want to define
a Toeplitz type correlation structure, but due to my inexperience with
programming in R, I feel a bit overwhelmed with the task at hand.

I understand that you can start with a function like corAR1 as template, but I
have no idea how I would define the methods (coef, corMatrix, and initialize) in
this context.

An example of code for a user-defined correlation structure would be very
helpful.

I did a search on Google and in the R-help archives, but have not found much in
terms of hints and specific examples for user defined correlation structures.

Thank you in advance!

Michael Jerosch-Herold