To set up a "shared folder" proceed this way:
1. Create a folder in your Home directory and call it vboxshared.
2. Type in Terminal:
3. Then in XP go to "Run" and type .
VBoxManage sharedfolder add "Windows XP" -name vboxshared -hostpath /home/yourname/vboxshared
4. Then type:
The name "Windows XP" is the name I have in GRUB.
net use x: \\vboxsvr\vboxshared
yourname= your home directory name.
Guest additions must be installed first.
You may have to put the contents of your USB stick into the shared folder.