R help - May 2006 - adding grid lines to an xyplot when there is only 1 panel

I've been struggling with this for a while and cannot get it to work.
Is there a simple way to add grid lines ---- I'd like to only add the
horizontal ones --- when using the groups argument in xyplot?
I can get the grid lines to plot, or the points/lines, but not both.
Here is a simple example of the sort of thing that I'm working with.
Thanks, in advance.

 >all
       est  STE AREA
   -0.229    V1   V1
   -1.129    V1   V2
   -2.084    V1   V4
   -2.918    V1   V3
   -0.548    V2   V1
   -0.217    V2   V2
   -1.937    V2   V3
   -1.205    V2   V4
   -4.126    V4   V1
   -1.481    V4   V2
   -2.070    V4   V3
   -0.042    V4   V4

xyplot(est ~ ISITE, data = all2, groups = AREA, type = "b",
  		auto.key = list(space = "right"))

Ken Knoblauch

-- 
Ken Knoblauch
Inserm U371
Cerveau et Vision
Dept. of Cognitive Neuroscience
18 avenue du Doyen Lépine
69500 Bron
France
tel: +33 (0)4 72 91 34 77
fax: +33 (0)4 72 91 34 61
portable: +33 (0)6 84 10 64 10
http://www.lyon.inserm.fr/371/

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