How can I repartition and format 'Toshiba USB 2.0 ext HDD USB device' containing CDFS partition?
Solution 1:
You can't delete the CDFS partition because it's not on the hard disk, it's on a write-protected flash memory chip (probably on the board inside the USB enclosure). It's there to provide some kind of feature from Toshiba, possibly OnSpec's password protection.
The "ClickFree" brand of USB hard drives have something similar. There's a post here of someone replacing the firmware with a version that doesn't use the flash memory. I couldn't find firmware for a Toshiba PX1220E-1G25.
Solution 2:
Partitioning of USB drives and support for multiple partitions is somewhat hit and miss and I'm not sure that you actually can easily do this from Windows XP. Try going to Control Panel, Administrative Tools, Computer Management, Disk Management. Select (carefully, you don't want to kill your machine) the USB drive and see if it will let you change the partition layout.
I do know that you cannot do it from command line (DiskPart), I suspect booting to a Linux utility DVD such as Knoppix would actually be easier.
The alternative would be to use a 3rd party utility such as BootICE. Note that I've not used this myself but it claims to be able to do it. Personally, I would use Linux but then I have a machine available.