[R] multiple line plots

[sosman]

I have some data in a CSV file:

time,pos,t,tl
15:23:44:350,M1_01,4511,1127
15:23:44:350,M1_02,4514,1128
15:23:44:350,M1_03,4503,1125
...
15:23:44:491,M2_01,4500,1125
15:23:44:491,M2_02,4496,1124
15:23:44:491,M2_03,4516,1129
...
15:23:44:710,M3_01,4504,1126
15:23:44:710,M3_02,4516,1129
15:23:44:710,M3_03,4498,1124
...

Each pos (eg M1_01) is an independent time series.  I would like to plot 
each time series as lines on a single plot and I wondered if there was 
something more straight forward than I was attempting.

I got as far as:

fname = 't100.csv'
t = read.csv(fname)
tpos = split(t, t$pos)
plot(tpos[["M1_01"]]$t, type='l')
for (p in names(tpos)) {
     lines(tpos[[p]]$t)
}

which seems to work but then I got stuck on how to make each line a 
different colour and figured that there might a be a one liner R command 
to do what I want.

Any tips would be appreciated.