Test post #Formatting the partitions
We will now format the partitions by putting a filesystem on and giving them the name 'ubuntu' (or any other name you want) and 'casper-rw' (this name is MANDATORY, do not change other names and do not use capital letters):
sudo mkfs.vfat -F 32 -n ubuntu /dev/sdX1
sudo mkfs.ext2 -b 4096 -L casper-rw /dev/sdX2
Mount the partitions on the drive. Take out the drive and put it back. Ubuntu Dapper or Edgy will mount the drive automatically if you have checked this option under System -->Preferences--> Removable media. Otherwise use 'mount':
sudo mount /dev/sdX1 /media/mountpointyouhave1
sudo mount /dev/sdX2 /media/mountpointyouhave2
On recent Ubuntu versions, the USB stick's partitions should simply appear under /media/ubuntu and /media/casper-rw if you have followed the proposed naming convention.