USB drive is indeed can be partitioned.
What you need to do is:
1. Unmount USB drive,
2. Disable auto-mounting
3. gparted /dev/sda
As I haven't been able to tame the automounting feature of Kubuntu, I used
Gparted-Live and partitioned from there. When I partitioned my USB drive in
Kubuntu, it persistently automounted the first partition (sda1) after it had
been created, even the whole partitioning process hadn't been finished yet.
Thus, it's the value of having a pocket-CD of Gparted-Live everywhere you go.
Now I have a 128MiB USB pen-drive partitioned into 80s MiB FAT16 and 30s MiB EXT2
250 GiB USB Harddrive partitioned into 40s GiB FAT32, and two 100s GiB EXT3
Now ... I am backing-up everything :-D