After my recent attempts to share a folder in Vista I may give you a little tip in case nothing works and all settings seem to be fine.
You need to allow connections incoming to TCP port 445 in the firewall settings. To do it, follow these steps:
- Open Control Panel → Windows Firewall.
- Click the Change settings link.
- Switch to the Exceptions tab.
- Click the Add port… button.
- Enter any description in the Name field and the number 445 in the Port number field.
- If you want to limit access to this port to specific hosts and/or subnets, click the Change scope… button and enter the appropriate values.
- Click OK and OK again to close the firewall settings window.