making a bootable usb stick

what ought to be a simple task has turned into a huge headache. the idea of a cool linux tablet being postponed, i thought i'd maybe update an old acer aspire one netbook i had in a closet. it was last booted, to kubuntu running a 2.6 kernel and kde-3.5.10, sometime in 2010. in that it has a 1.6 mHz chip and a gig of memory on a 120-gig drive, it seemed a good machine for a Q4OS experiment. (the experiment part being whether i can keep my kde settings -- i have never enjoyed reconfiguring.) so i d/led the .iso for the current stable Q4OS, no problem. it's getting it onto a USB stick that's killing me. reason is, when i insert the USB drive, it automounts and refuses to unmount, and one apparently cannot make a bootable disk onto a mounted drive. i've tried a couple of programs in hope of burning the bootable stick -- the ubuntu startup disk creator and something called unetbootin. they both blow up, apparently because the stick is mounted. the little icon for the usb stick that appears at the top left of my monitor has the green line saying it's mounted. i right click and click "unmount" and either nothing happens or the green line disappears only to reappear soon thereafter. and if i try to umount it, i'm told it's busy. in my younger days one or more pieces of equipment would by now have flown across the room and smashed into the far wall, but i'm older and calmer now. so it is merely driving me insane. there's got to be a way to get the image onto the usb drive and make it bootable, but i'm damned if i can find it, with automount confounding me at every turn. (i'm not interested in turning off automount forever -- i'm a photographer and not having to manually mount sd cards is a wonderful thing.) anybody here have any ideas? -- dep The shortest distance between you and playing great acoustic guitar: the great new instructional DVDs from Marjorie Thompson, available at www.MarjorieThompson.com