Okay, riddle me this:
My laptop can (via Windows file sharing) log in to my desktop and get at the shared folders.
My desktop can't log in to the laptop.
Both are using the same username with the same password on the same version of Windows XP. Not only should this Just Work, but it indeed has Just Worked every time I've done this before. So I'm at a loss as to why it's failing now.
My computers never have simple problems...