Anyway, if you've got some strings and you want dates, use
But if you want datetimes (i.e. don't want to lose the time component), use
Also, subset is nice:
subset(dat1, (t > '2009-01-01') & (t < '2009-01-05'))
Create a frame:
#make up some data
x = seq(-2*pi, 2*pi, by = 0.05)
#create the frame
datx = data.frame(x=x)
#add another column
datx$sinx = sin(datx$x)
#show the columns
#gives:  "x" "sinx"
See also http://www.statmethods.net/input/datatypes.html for a nice brief intro to R's different structures.