[R] Multiple series plot with different 'type' argument

[Ruben Roa]

Hi:
I need to plot two time series in the same plot and
they cover the same time range and have the same 
frequency. With 
RSiteSearch("multiple series plot") 
i found this post by Gabor Grothendieck:
http://finzi.psych.upenn.edu/R/Rhelp02a/archive/42281.html
Exactly what i need except for one detail. I want one series
to be made of points and the other by a line. When I simply
try:
xts <- ts(x$b,start=x$a[1]) 
yts <- ts(y$b,start=y$a[1]) 
ts.plot(xts,yts,type=c("p","l"))
or if i use the 'type' argument inside gpars=list()
i get an error of "invalid plot type".
Then if i try
ts.plot(xts,yts,type1="p",type2="l")
i get warnings about NAs introduced by coercion and the
plot still shows two lines.
Is there any other way i can get these two time series
in the same plot one with points and the other with lines?
Any help much appreciated.
Ruben