You need to look at ?axis. Try this:
y <- c(-4,3,-2,1)
x <- c("time 1", "time 2", "time 3", "time 4")
plot(seq(1,length(x), by = 1), y, type = "b", axes = FALSE, xlab =
"Times", ylab = "Stuff")
axis(1, at = seq(1,length(x), by = 1), labels = x)
axis(2)
HTH, Andy