Photo and Flash Drive problems

Hi
I am an amateur photographer and I having a problem transferring photos
(mostly jpegs) from my computer (and from my external hard drive) to flash
drives The problem is, when I copy photos to the flash drives about
one-tenth of them become corrupted. If I copy 500 perfectly fine photos,
fifty will be corrupted. The corruption can be anything from a line of
misplaced pixels, to a top half of a photo mixed with the bottom half, to
whole photos grayed out. When I use my computer with XP, no problem. I can
copy hundreds of photo at a time without a single corruption. But, with my
computer that uses Vista (Home Premium with SP 1), I get the corrupted
photos. Both computers are desktops and made locally. The Vista computer is
a 64 bit system with an AMD Athlon 64x2 Dual Core processor. It has 4GB of
Ram. The external hard drive is a Western Digital (USB). The flash drives
are either SanDisk or Kingston. Can anyone help?
blue17