Generating axes with "Sun Apr 20 22:45:27 PDT 2003" time coordinates.

Good Morning!

My apologies for what may be considered an infantile question: I have data 
that I would like to plot, positive integers for the y-axis, and time 
coordinates of the "Sun Apr 20 22:45:27 PDT 2003" format for the x-axis.
I have tried:

x1 <- 1050352610
x2 <- 1050352999
x3 <- 1050858319
class(x1) <- "POSIXct"
class(x2) <- "POSIXct"
class(x3) <- "POSIXct"
X <- c(x1, x2, x3)
...
...
plot(X, Y, type = "l")

I end up with "Mon", "Tues", "Wed", ... x-axis coordinates, when I need 
"2003-04-14 13:36:50 PDT",  "2003-04-14 13:43:19 PDT"
and  "2003-04-20 10:05:19 PDT" x-axis coordinates. I adjusted the data to be 
one second apart and ended up with integer "19", "20", ... x-axis 
coordinates. What do I need to do to accomplish this? Any help will be 
greatly appreciated, as I have looked at the help pages, and the web, to no 
avail. I would also be more than happy to purchase a book that contains 
information to this level of detail if that is available.

Thank You,

John Jaynes