See ?boxplot for all the help you need.
outline: if ‘outline’ is not true, the outliers are not drawn (as
points whereas S+ uses lines).
boxplot(x,horizontal=TRUE,axes=FALSE,outline=FALSE)
And for extending the range of the whiskers and suppressing the outliers inside this range:
range: this determines how far the plot whiskers extend out from the
box. If ‘range’ is positive, the whiskers extend to the most
extreme data point which is no more than ‘range’ times the
interquartile range from the box. A value of zero causes the
whiskers to extend to the data extremes.
# change the value of range to change the whisker length
boxplot(x,horizontal=TRUE,axes=FALSE,range=2)