Really really dumb problem (sorry)

I just bought Parallels Desktop for Mac and I'm trying to migrate my PC to my new Macbook Pro. I've installed Parallels Desktop on the Macbook and Parallels Transporter Agent on a Dell Inspiron 9100 laptop running XP home edition, which are both on the same LAN. However, I can't get the migration to work. I know it sounds dumb, but I can't even make the initial connection between the two machines.

I fire up PTA on the Dell, and it says a network connection is available. Then, on the Macbook, I select Import from the PD File menu and get the Welcome to Parallels Transporter screen. I hit Continue, and get the Migration Source Type screen. I select Physical Computer and hit continue to get to the Migration Method screen. I select Network and hit continue to get to the Connecting to Parallels Transporter Agent screen. The Dell's IP address is visible, so I select it and hit continue. So far, so good.

Now, I get a dialog box saying 'The computer LAPTOP1 (i.e. the Dell) requires authentication'. But the problem is, it doesn't. It has never had any password protection, nor even an Administrator name. I have never had to log in at start up, and I have never had to give any user name or password in order to access it as a guest from anywhere else on the network. In other words, there is no name or password that I can enter in the Parallels Transporter dialog box. So the question is, how do I get past this point? I even tried giving the Dell an administrator name and password, just so I could enter something, but Parallels Transporter refused to recognise it. Help!

Thanks, Chris