I received my Pi a couple of days ago and I have got it working with two SD cards, each 4GB. On the first it goes to the GUI, while on the other I have installed webmin and I run the Pi headless (that means with no display, keyboard or mouse, right?).
So far so good. Now I notice that only about 2GB of the 4GB is used, and that there is very little free space in that 2GB. So I would like to increase the partition size. (Or perhaps create another partition that Linux could use, but that is more likely to get complicated, I think). I have a spare PC on which I can run Ubuntu from a CD, and I can plug in the SD card via a USB adaptor. Ubuntu sees the partitions, but it complains that they are read-only. I have checked that the write-protect is off, and I have tried with other (non-Pi) SD cards and can write to those.
Is there something special about the Pi partitions that makes them readonly on another system? What do I do now?