Windows 7 Partition Problems

Now, I know Windows 7 has a hard time reading Vista partitions (which can easily be fixed by manually assigning a drive letter to that partition) but I have a different problem.

I have a 1TB External drive, with all my backups, software etc on it. The partition was created in Vista, a normal NTFS partition. It works well under XP as well.

But Windows 7....*sigh*...it detects the drive, assigns a drive letter as well, but when I try to browse the drive, it says that it is not formatted, and needs to be formatted. Take the drive out, plug it into a Vista or XP system, and it works no problem.

Any suggestions, ideas?