It's actually not all that hard.
You have to set permissions in the share's properties dialog box under both the sharing tab as well as the security tab, as when shares are accessed across the network share permissions are merged with NTFS (security) permissions and the most restrictive wins.... so mind your group memberships as a specific user can be granted full control, but if the "Users" group only has read then read is all he is going to get if he is a member of that group.
Additionally when prompted for credentials you'll need to use the MachineName\Username format and tick the box that says remember credentials. Like ......
MyWinMachine\MyUserName (MyWinMachine = The machine name hosting the share) (MyUserName = An account...