The "USB Startup Disk Creator" seems to be a bit fussy about the flash disk
it uses. My system wouldn't go past the "Format" button with a 1 GB flash,
but worked with a 2 GB, yet the 1 GB one seems to hold other data fine and
it was certainly large enough for the installation files.

I've had more success with a burned CD running from an external USB CD/DVD
reader. If you don't have one you can buy a case fairly cheaply (about $20)
and temporarily put the burner/reader from your desktop system into it. Even
the most recent systems sometimes choke on booting from a flash drive and do
better on a USB Disk.