Vista - Backing Up to Network Drive?

I have a 1 TB external hard drive connected to my network. I would like to back up my laptop and setup automatic backup on a weekly basis to this drive like I have done with my desktop. However, the damned thing keeps asking me for a username and password that I did NOT set up on the computer that has the hard drive connected directly into it. When I use my Windows username and password for the computer the drive is connected to, it tells me it is invalid. So what, exactly, is the password if that isn't it?

I have password protection turned OFF on my network, so it shouldn't even ask me for one.

Are all the machines Vista?

Indeed, and both are Home Premium 32bit. They're pretty much the same computer, just one is a laptop. One IS SP1 while the other is not (since HP refuses to offer new drivers for the finger print scanner).

I think that when you schedule a task in the task manager, it asks you for a password.
Try to enter a new task in the manager and i'm pretty sure it will ask you for a password.

Try Acronis. It does it all.

That's great, but it doesn't explain why my laptop is being prompted for a password when trying to back to the a drive that isn't physically connected to it.