Live OneCare Tip: If you switched to Live OneCare recently like I have (it's cheaper, faster, and uses less resources), you might find that OneCare Firewall blocks Windows File/Printer Sharing due to a bug. To unblock file/print sharing service, trying this:

1. Open Windows Live OneCare window
2. Open "Other Tasks" >> "View or change settings" [hideous obscuring of key functionality IMHO]
3. Switch to "Firewall" panel then click on "Advanced settings" button
4. You should be at "Firewall Advanced Settings" panel.
5. Change the top set of radio buttons to the setting you want (I use "subnet only") then click "Apply".
6. If that didn't work, try toggling ("Do not share…", "Apply", "Only share…", Apply).

Above steps allowed me to access Windows shared folders from my MBP again recently.