Rotating the x-axis labels of a barplot

Dear listserv,

Here is my latest formatting problem. I would like to rotate the x-axis labels
by 45 degrees on a _barplot_. Apparently this is slightly different from the
example given in the R FAQ, which is for rotating the x-axis labels on a
scatterplot
(http://cran.r-project.org/doc/FAQ/R-FAQ.html#How-can-I-create-rotated-axis-labels_003f).


I have adapted that code, as best I could, and here is what I have come up with
so far:

x <- c(4, 1, 1, 1)
barplot(x, space = 0)
#the "space = 0" argument, above, just reflects my personal preference for
having no space between the bars
text(1:4, par("usr")[3] - 0.025, srt = 45, adj = 1, labels = c("< 750",
"750-1000", "1000-1250", "> 1250"), xpd = TRUE, font = 2)

The graph this generates is pretty close to what I want, but here's where I'm
stuck: How do I move the x-axis labels to the _center_ of each bar? Right now,
they line up with the right-side of each bar.