Win 7: Backup notebook to desktop using Homegroup?

I'm trying to set things up so I can backup my notebook PC (Win 7 Ultimate 64-bit) to my main desktop PC (Win 7 Enterprise 64-bit).

In theory, Microsoft states this is possible. Both PCs are on the same Homegroup and I can access files between them. The problem starts when I try to setup Win 7 backup on the notebook.

Neither PC has password protection set up in Windows. Initially, I tried to set things up to back up into a "My Documents>VIAO PC" folder - no luck. I even tried setting up a second admin. level user account ("VIAO Backup") strictly for the backups - again, no luck.

Since I have over 1TB of free space on my main PC (and only about 40GB of files on my notebook), I'd like to set this up to run every evening through my Wi-Fi. Any ideas on what I'm missing in order to get this to work?

Thanks in advance for your help.