Writing to USB key

[Thomas Beckett]

I have 1 USB 1 key that works fine and my muvo also works just fine,
but I also have a Sony 256MB USB2 key. When I plug it in it is
detected fine (icon shows on desktop and I can open a nautilus window)
but when I open it the files are not listed at all and when I try to
write something to it, say copying a folder across to it. It seems to
copy - the copy box disappears without any errors at all. But when i
look again, the directory listing is still blank. I booted up my
girlfriends windows laptop and I can see i directory tree full of
files and folders on it, the strange thing is that the folder HAS been
created but the files have not copied across into it, just the folder
created.
I then tried to copy the folder over from inside windows (after moving
it to windows with my other usb key) and replacing the folder when it
asks to overwrite. The windows machine just blue screens and resets
completely!! - I then logged back into XP again and deleted the folder
on the USB key. Then I copied the folder from windows and it copied
fine!

Any help would be greately apreciated. 

Tom