[R] simple predict question

[sms13+@pitt.edu]

Excuse the simple question...
I'm not sure what I'm doing wrong with predict, but let me use this example:
Suppose I do:
dat<-matrix(c(0,0,10,20),2,byrow=T)
lm1<-lm(dat[,2]~dat[,1])

Suppose I want to generate the linearly-interpolated y-values between the 
point (0,0) and (0,20) at every unit interval.
I thought I just do:
predict(lm1, data.frame(seq(0,10,1))) to get 0,2,4,6...,18,20, but instead 
I just get:
1    2
0  20

Any suggestions?

Thanks,
Steven