Replacing several rows of a matrix at once

Hello Folks.  This must be a silly question with a (not) obvious (to me)
answer.

Consider this:

tmp <- matrix(1:200, nrow = 20)
vec <- 300:309

tmp[9,] <- vec # replacing one row works fine

p <- c(3, 11, 17)
tmp[p,] <- vec
# replacing multple rows pastes the values down a column and recycles vec.

What I want to do is replace multiple rows simultaneously at once.  I
suppose I can write a function, but this seems pretty fundamental so I feel
I must be missing some obvious alternative.  I'm feeling like I'm in the
Inferno!

TIA.  Bryan
*************
Bryan Hanson
Professor of Chemistry & Biochemistry
DePauw University, Greencastle IN USA

sessionInfo()

R version 2.12.0 (2010-10-15)
Platform: x86_64-apple-darwin9.8.0/x86_64 (64-bit)

locale:
[1] en_US.UTF-8/en_US.UTF-8/C/C/en_US.UTF-8/en_US.UTF-8

attached base packages:
 [1] splines   datasets  tools     grid      grDevices graphics  utils
stats    
 [9] methods   base

other attached packages:
 [1] survival_2.35-8    gridExtra_0.7      GGally_0.2.2       xtable_1.5-6
 [5] mvbutils_2.5.1     ggplot2_0.8.8      proto_0.3-8        reshape_0.8.3
 [9] ChemoSpec_1.46     seriation_1.0-2    colorspace_1.0-1   TSP_1.0-1
[13] R.utils_1.5.3      R.oo_1.7.4         R.methodsS3_1.2.1  rgl_0.92.794
[17] lattice_0.19-13    mvoutlier_1.4      plyr_1.2.1
RColorBrewer_1.0-2
[21] chemometrics_1.0   som_0.3-5          robustbase_0.5-0-1 rpart_3.1-46
[25] pls_2.1-0          pcaPP_1.8-3        mvtnorm_0.9-92     nnet_7.3-1
[29] mclust_3.4.6       MASS_7.3-8         lars_0.9-7         gclus_1.3
[33] cluster_1.13.1     e1071_1.5-24       class_7.3-2