Retrieve specific y for a list of x on a ploted line

Dear list,

I'm trying to retrieve specific y for a list of x on a drawn line in the
plot area.
The line is plot with an other list of xy coordinates,which only serve to
plot the line.
Here is an example of the beginning of a table of initial coordinates which
permit to draw the line:
         X     Y
"1"    0    137.659166666667
"2"    2.502    152.623333333333
"3"    4.998    162.391333333333
"4"    7.501    170.753666666667
"5"    9.997    174.877
"6"    12.499    178.4275
"7"    15.002    184.565
"8"    17.498    189.8985
"9"    20    192.6885
[...]

Here is what I want to do:

         dossier<-  ### path of the table to read
         table <- read.table(dossier)
         curv<-plot(smooth.spline(table), type="l",xlim=c(0,100),ylim=c(0,255))

         # Now the line is drawn

         #For x in 1:100 on  curv, I want to retrieve each
corresponding y and sort coordinates in a table.

I search on the forum, the RSiteSearch, the R-intro.pdf, and I read the book
of the most common graph packages...
But I don't find the specific answer for my problem.
Can you help me, please.
Kind regards

Camille