For printer sharing in OneCare to work, the printer must be shared via OneCare on the PC that has the printer connected to it and the PCs that will be using this printer must be using an OS of the same type as the host PC. If the laptop is using Vista 64 bit edition and the desktop is running Vista 32 bit edition, sharing will not work. A PC with XP 32 bit and Vista 32 bit can share printers using OneCare printer sharing, too.
OneCare cannot share a printer that is not connected to one of the PCs in the Circle, that is a wireless printer or a network printer.
It is possible that your laptop is not seen to be on the same subnet within your network based on the way your router works, if the laptop is wirelessly connected. You may be able to change the sharing settings by doing the following:
Open OneCare on each of the computers.
Click Change Settings
On the firewall tab, click configure firewall
If the network is shown as Public, click Change Location to change it to "Home or Work."
Click the Advanced Settings button
Click Network connections tab.
If there are multiple active connections shown, you may need to disable the extras in your Windows network connections settings. (Network and Sharing Center, manage connections, in Vista; Right click My Network Places and select Properties on the Start menu in XP)
On the Ports and Protocols tab, add a check mark next to File and Printer Sharing - for subnet and Internet if the first setting alone (after all of the above are verified) does not allow Sharing to work.
Note that you may need to share the printer manually, not using the OneCare printer sharing feature if you do the above or if your computers are not using the same architecture (32 bit/64 bit).
If all of the above fail, please contact support.
How to reach support (FAQ) - http://social.microsoft.com/Forums/en-US/onecareinstallandactivate/thread/30400b52-7f26-4ba0-bc18-17e305329d90
-steve
Microsoft MVP Windows Live / Windows Live OneCare Forum Moderator
