I've got a USB 2.0 hard drive I've been using with a computer running
Windows 2000. I think it's using the new Windows 2000 file system, but
I'm not sure. I'd like to be able to access those files from a
computer running Windows ME, so I tried simply plugging the USB drive
into that other computer. After installing some drivers, it recognized
the drive, but it thinks the drive is unformatted, and it won't let me
open it without formatting it first. I'm guessing that, since it's
Windows ME, it can't recognize the Windows 2000 file system, and
that's why it thinks it's unformatted. Or maybe it just assumes all
new USB drives are unformatted until it formats them. These are just
guesses. Is there anything I can do to allow myself to access the
existing files on this USB drive from the computer running Windows ME?

If you still have the Win2K machine around, you can verify if the
drive was originally formatted with NTFS:
Bring up file explorer (Start-E) or go to My Computer, right-click on
the drive in question and select Properties.  Under the General tab,
you will see the File System: label, and that will say NTFS, FAT or
whatever.

If it is NTFS, you might (dunno if it works with USB) be able to load
this free software from SysInternals on WinME to gain Read Only access
to the drive.

http://www.sysinternals.com/ntw2k/freeware/ntfswin98.shtml

You'll need some files from a Win2K machine to get it going (read all
the instructions on the page).

One thing you couuld try is moving the files from the USB drive to a
folder on your 2000 box and then reformating the USB drive to FAT or
FAT32 which your ME and 2000 box will recognize. Then put the files
back onto the USB drive.