Its function and yahoo

from the perspective a newbie it seems  get.hist.quote() works
reasonably well.

Please read this thread why I think that it should be improved.

my issues come with (I think) the plot() part where the documentation
doesn't seem to provide the solutions.

Consider the following...

x <- get.hist.quote(instrument = "CPN", quote = c("Ad", "Vol"), start
= "2004-01-01"); plot(x, main = "Calpine",type='l')

And in which way is this not behaving as documented? If you should be
referring to the gaps, this is due to NAs. But you could do

z <- get.hist.quote(instrument = "CPN", quote = c("Ad", "Vol"),
  start = "2004-01-01", origin = "1970-01-01")
z <- as.zoo(z)
index(z) <- as.Date(index(z))
z <- na.omit(z)
plot(z)

to obtain a "zoo" object without NAs. Note, that I already pointed you
to this example.

Hoow would I 
a) have the date appear in years or months etc 

Look at ?aggregate.zoo and look into the archives of this mailing list.

b) have the top part in semi-log form (so % changes are of equal
vertical distances) and c) get the volume to scale down (say in
millions of shares vs shares)

z[,"Volume"] <- z[,"Volume"]/1000000

and btw:

fortune("WTFM")

This is all documented in TFM. Those who WTFM don't want to have to WTFM
again on the mailing list. RTFM.
   -- Barry Rowlingson
      R-help (October 2003)

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