So guess what? Trying to authenticate remotely was a bad idea. I mean, it could work in theory, but in practice there's a simpler solution. We tried running the script directly on the server, and it worked! We had to comment out the block of code that was trying to log us in, but as soon as we did that, we had a waterfall of links being spidered.
Now I just have to wait for my supervisor to give me access to that server. Until then, I'll have to work on the VBScript side of things. The VBScript is basically done, but I have some issues that need to be refined - one of which popped up after building classes to group similar variables and methods.
Once I get to work on the spider again, it looks like I have to refine it to only stay on our intranet. It got a bit carried away and started spidering some external links. It's possible it may have spidered a better portion of the Internet if we let it.