I'll admit I just saw the article, briefly looked at it, and pasted it. And that article is probably wrong, as this snippet from Wikipedia shows:
Symbolic links are different from hard links. Hard links do not link paths on different volumes or file systems, whereas symbolic links may point to any file or directory irrespective of the volumes on which the link and target reside. Hard links always refer to an existing file, whereas symbolic links may contain an arbitrary path that does not point to anything.
And if you want to know the jist of what a symbolic link is:
A symbolic link contains a text string that is automatically interpreted and followed by the operating system as a path to another file or directory. This other file or directory is called the "target". The symbolic link is a second file that exists independently of its target. If a symbolic link is deleted, its target remains unaffected. If a symbolic link points to a target, and sometime later that target is moved, renamed or deleted, the symbolic link is not automatically updated or deleted, but continues to exist and still points to the old target, now a non-existing location or file. Symbolic links pointing to moved or non-existing targets are sometimes called broken, orphaned, dead, or dangling.
In layman's terms, a symbolic link is essentially another kind of shortcut to a file or directory. You want to use a symbolic link, not a hard link.
And about the whole free space thing, say you have a symbolic link directory junction named Foobar in C:\ that points to D:\Foobar. When you open up Foobar, Explorer will say C:\Foobar. But anything you do in here doesn't affect the C:\ partition, it goes to D:\Foobar transparently. But since Explorer (or any program) thinks it's still in C:\, it will use C:\'s stats for looking up free space, not D:\'s.