generating a data frame with a subset from another data frame

R gurus,

I have a data set that looks something like this:

Site    Species DBH     #Vines
G       PLOC    45.9    4
G       ACNE    23.3    1
G       ACNE    12.0    0
G       FRAM    35.9    5
G       AEGL    11.2    2
N       PLOC    77.3    12
N       JUNI    78.6    7
N       ACNE    18.9    1
N       ACNE    15.7    3
N       ACRU    35.5    4
H       ACSA2   24.1    6
H       ULAM    35.2    7

There are 730 individual trees (22 species) from four sites in the
actual data set.  I would like to create a second data frame that
contains just the most common species (mainly ACNE, PLOC, ULAM, FRAM,
and ACSA2).  Here's some of my attempts:

 >study.1<-subset(study,study$Species=c

("ACNE","PLOC","FRAM","ULAM","ACSA2))
Error: syntax error

 >study.1<-study[study$Species==,c("ACNE","PLOC","FRAM","ULAM","ACSA2)]

Error: syntax error

 >study.1<-study[c("ACNE","PLOC","FRAM","ULAM","ACSA2"),]

#This one appeared to work, but upon inspection, it just copied the
entire "study" data frame instead of just copying the data I wanted,
as study.1$Species had a length of 22 (the same as the original)
instead of the desired length of 5.

I've already consulted a book on R as well as spent the last three
hours searching the R-help archives.  There must be a way to get the
subset I desire but it is not obvious to me.

Thanks in advance for your help.

Jim Milks

Graduate Student
Environmental Sciences Ph.D. Program
Wright State University
3640 Colonel Glenn Hwy
Dayton, OH 45431