Expand it how? Assuming you mean you want to create a filesystem on your unused partitions, then...
fdisk -l (FDISK -L lowercase)
Find the partition that is not formatted then;
mke2fs -j /dev/hdx
where /dev/hdx is the partition needing formatting.
If you mean you want to merge the unused space into an existing partition, you should check out parted at www.freshmeat.net