Matching rows in a Data set? I'm Stuck!!

 What i really want to do is write an R script that says "if the ID of
 dataset1 and 2 match (2nd row), print out that whole row into a new
 dataset3".

Would this do what you want?

x1 <- iris[1:5,]
x1

Sepal.Length Sepal.Width Petal.Length Petal.Width Species
1          5.1         3.5          1.4         0.2  setosa
2          4.9         3.0          1.4         0.2  setosa
3          4.7         3.2          1.3         0.2  setosa
4          4.6         3.1          1.5         0.2  setosa
5          5.0         3.6          1.4         0.2  setosa

x2 <- iris[4:7,]
x2

Sepal.Length Sepal.Width Petal.Length Petal.Width Species
4          4.6         3.1          1.5         0.2  setosa
5          5.0         3.6          1.4         0.2  setosa
6          5.4         3.9          1.7         0.4  setosa
7          4.6         3.4          1.4         0.3  setosa

x.ids <- intersect(rownames(x1), rownames(x2))
x.ids

[1] "4" "5"

x3 <- cbind(x1[x.ids, ], x2[x.ids, ])

Liviu