NUL is an amusing little file because it cannot be deleted. As described in c:\nul\nul, it is one of the DOS Device files. Because of this, any attempt to delete NUL results in a failure.
The worst part about the whole thing, though, is that when the file is created, people can put data into it. So you can get a gigabyte undeletable file on your hard drive, or more amusingly, some one else's hard drive. (I had someone do this to me at a LAN party recently. Rick, you will die.)
How do you create a little treasure like NUL? Apparently, it's easy to do over file sharing - I'm not clear on the exact process (and I don't think I would post it up here, anyway - if you're not smart enough to figure this out on your own, you shouldn't be doing it), but I think the trick is to create a file, then rename it to NUL. But don't quote me on that.
Curiously, Win2k is affected by this problem, just like everybody else. I know this because I run Win2k. I haven't yet fixed the problem - if anyone feels generous enough to help me out, /msg s_alanet. I'll also post the solution that worked for me in this wu.
In response to Wicker808's comment: The same goes for nul which insinuates, incorrectly, that NUL is a file, which it isn't, and that it stores data, which it doesn't. You should really research your nodes before writing them up.
I've sat on that /msg for some time now, and here is my response:
I realize that NUL is not a file, anymore than /dev/null is a file. HOWEVER, because of the slightly imbalanced implementation of Microsoft NTFS, (and presumably FAT32) file systems, it is possible to, in fact, create a NUL file - one with a name of NUL. And once this file has been created, it is nearly impossible to remove for the reasons outlined above.
If you want to "discuss" this further, I can send you a screenshot of the folder where some friends of mine created a NUL file on my Win2k system at a LAN party.
Your wu is clearly more informative, although I think that a pointer to DOS Device Files is just as effective, and more inducive to a cohesive database.