Perineum, I double checked and that's the method I used, well almost. The "Share" button is greyed out on my machines (googling around it seems to be a common thing) so I go in through the "Advanced Share" button, into 'Permissions' and set 'Everyone' access to full control. all other steps including the 'Network and Sharing Center' are the same. And that doesn't work for me. Thanks for taking the effort to list it out though.
But I did get it figured out!!! <pats self on back> The answer lies NOT under the 'Sharing' tab BUT under the 'Security' tab of the properties window. Under that tab you'll see a list in the 'Group or User Names' window. I had Authenticated Users, SYSTEM, Administrators (MAIN\Administrators), and Users (MAIN\Users). Under that window I clicked 'Edit' and then a new window pops up and under the list I clicked 'Add', typed in "everyone" and set permissions in the same popup window to Full Control and voila! It all works! Did the same steps on the Vista machine too and all went perfect.