Hi leachim
There is a freeware program that helps Win9x/Me systems read NTSF drives ---
http://www.diskinternals.com/products/ntfs-reader/
But I imagine you'll have to make sure that the USB drive can be detected in Windows Me (regardless of its file format ... it's a matter of USB device support). If your USB external drive has a Win9x/Me driver available for download, try that).
I'm assuming that you are referring to a USB external hard drive, and not a USB flash-memory drive. Most USB flash-memory drives (also called "pen drives") are formatted using the FAT file system, which WinMe would have no trouble reading.
Best of luck
. . . Gary