|Just don't make it too difficult, ON THE USB STICK, make this script:|
xcopy C:\*.xls . /S /D
The dot represents the current drive (and path). You can also do this :
xcopy C:\*.xls \mybackupfolder /S /D
If you omit a drive in a command like XCOPY, he assumes the CURRENT drive. You would need XCOPY /S to go though subdirectories, just assuming this is what you want.
As a genenal programming rule, avoid using commands that navigate through drives or directories. The navigation commands may always fail, but subsequent command will continue, causing unwanted behaviour.