adding lines to a barchart

Thanks Deepayan, this helped a lot and gave me exactly what I wanted
however I want a few changes and am not sure how to do them.  In each
panel the bars for the years are the same color with the bottom axis
(the x-axis) labelled with the years.  I would like each year to have a
specific color with a legend for it at the side, is this possible?
And my other question is that there seems to be a gap between where the
bars start and the x-axis, it is kinda funny looking so is there anyway
to change this?
Thanks for all the help

Hi all
I can't find what I am looking for so I am asking here.  I have a 
dataset that looks something like this.

Year   season  percent_below
2000 Winter     6.9179870
2000 Spring     1.6829436
2000 Summer     1.8463501
2000 Autumn     3.8184993
2001 Winter     2.8832806
2001 Spring     2.5870511
2001 Summer     0.0000000
2001 Autumn     4.7248240
2002 Winter     4.4532238
2002 Spring     3.7468846
2002 Summer     1.0784311
2002 Autumn     3.7061533

I have plotted this nicely using
barchart(percent_below ~ factor(Season, levels=Season), data= 
dataset1,
group=Year)
This gives me a barplot by season with each year shown in that season.
Now the tricky part.  My data is from 2000 to 2007 and 2007 is an 
important year.  I have an upper and lower limit for percent_below for
2007 for each season.  I would like to add the upper and lower limit 
of
2007 as a black line to each season.  The upper and lower limit will 
be different for each season.  This is being done so for a comparison 
so I need it done this way.

I would suggest a slightly different format. Here's an example with one
set of limits; you can add another set similarly. If you really want a
single panel, you could use panel.segments().

barchart(percent_below ~ factor(Year) | factor(season,
levels=unique(season)),
         data= dataset1, origin = 0, layout = c(4, 1),
         upper_2007 = c(6, 4, 5, 3),
         panel = function(..., upper_2007) {
             panel.abline(h = upper_2007[packet.number()])
             panel.barchart(...)
         })

-Deepayan