then I may use the remainer flash memory by any way or not ?
 

when I make a USB BOOTABLE with kubuntu 8.10 from a live CD, if I choose to use HALF USB MEMORY Space, then I may use the remainer flash memory by any way or not ?

Yes you may. You can use it as storage space to share files between other systems.

Some LQ members are having a similar discussion in the Downloading Linux to flash drive thread. It looks like a few folks are just getting started with this project at about the same time! Admittedly, in that thread, I could have been more clear on the specific point you're raising here, or refrained from commenting where I had little experience to contribute with.

I understand that you are likely limited to using recent distribution versions for such a purpose and may favor Ubuntu as a candidate, but just so you know some have found version 8.10 of Ubuntu to be less than stable in their experience. It might be worth reading the thread I'm in love just to have a frame of reference.

if i choose linux use half space, it will created two drive letters eg e:/ and g:/ or
 

You say: "Yes you may. You can use it as storage space to share files between other systems."

well, if i choose linux use half space, it will created two drive letters eg e:/ and g:/ or... ? how access non linux part of USB STICK ?

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well, if i choose linux use half space, it will created two drive letters eg e:/ and g:/ or... ? how access non linux part of USB STICK ?

if i choose half stick i make two partitions , one linux and one unused like a hard drive ? may install in one kubuntu and to other ubuntu ? only one partition may boot the first ?

Do you want to install both flavours of *buntu on your memory stick? In the absence of someone posting that it works, give it a try. The installs will/should detect the presence of another op/sys and make the required grub adjustments to enable booting between the two.