a simple plot problem

R users;

This is the case, I
want to plot for example Dow Jones Ind Average versus
Time (Time on X-axis) , I use Plot(t,djia) (t is for
time and djia for dow jones), and then I use lines(t,
djia) to make it a line type of graph. however it
takes   
a long time to graph this line because I think it
plots it point by point, on the other hand if I use
tsPlot from fBasics package, on the x-axis I don't get
time value. ( I know that tsPlot is for time series
objects, but I dont know how to convert my data.frame
data to a time series data type in a way that I get my
DATE column to be substitute in the x axis)

Thanks for your help,

Sean