[R-SIG-Finance] XTS - plot 8 years by month

[James]

Hi,

I have an xts object with eight years of monthly calculations, so a  
total of 96 pieces of data.  What I would like to do is to plot 8  
lines, one for each year, with each months data aligned along the x  
axis.  So the x axis would be each month, from Jan to Dec.  I tried  
using monthplot but it creates 12 lines for each of the months, not  
what I want.

I know I can pull each years data by z['2000'].
 > z['2000']

2000-01-21 0.2694149
2000-02-18 0.2404871
2000-03-17 0.2756291
2000-04-21 0.2959471
2000-05-19 0.2736563
2000-06-16 0.2056082
2000-07-21 0.1621791
2000-08-18 0.1382985
2000-09-15 0.1333139
2000-10-20 0.2556851
2000-11-17 0.2216605
2000-12-15 0.2704414

Does anyone know of an easy way to do this or do I have to create a  
new data.frame with months by years?  Thanks.

James