unable to copy files to ext3 partition of sd card

In the course of the installation process after partitioning the sd
card i am not able to copy the root file system to the ext3 partition
of the memory card. please help.

I've had to use sudo before I could copy any files to my SD card in
Ubuntu 11.10. For example:

sudo nautilus

gives me a GUI that has access to copy files to the SD card where
nautilus by itself cannot.