Vista - Backup & Restore won't backup to shared drive

When backing up using OneCare to a shared drive on an XP Media Center Edition
PC (Or even using the Windows Easy Transfer), it works without issues.
When I back up to the same XP Media Center Edition PC using the Vista Backup
& Restore (Which is what I'd prefer mainly because of Shadowcopy) The first
time I try to do the backup, first it asks for a username and password.
Niether this PC, or the one I'm backing up to have passwords set up but it
won't let me continue without a password. I set up a password on both
machines as a test, and tried it without them It always goes to the next
step. It scans the files for backup, and then right after it gets to the
point where it should be transfering files, it tells me the location cannot
be found. All it puts in the folder is a file called MediaID.bin
If I click the "try again" option it skips the scanning portion, goes right
into the backup and then pops up with an "Access is denied" option. If I
delete the MediaID.bin file, it scans again, and then brings up the location
cannot be found error.
I've tried multiple folders on this machine, each time OneCare backup works,
but Vista Backup doesn't.

Also, I tried the instructions on this page
http://www.jimmah.com/vista/net/ntlm.aspx which was listed in another thread
with similar issues, but it didn't seem to work.
Is this a known issue? Is there a way around it? Any suggestions?