[R] Zero is not zero

[szhan@uoguelph.ca]

Hello, There:
I read data from tab-delimted text file(1888.txt) in C:/temp, which has 
thousands rows and 80 colulms, using read.delim("C:/temp/1888.txt"). when I 
retrieved the numeric coulum which has real zero values and applies R buid-in 
function such as mean( ), sum() and got a result of NA. It seems that R (R 
1.6.2 in windows) considers zero as missing value (NA). Thus my question is 
how to read the real zero as zero.
Thank in advance.

Joshua