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 that exists on the machine hosting the share, that has appropriate permissions to access the share)
Password (Password = The password word for that user, that he uses to log on to that machine that is hosting the share)
Alternately place identical usernames and passwords on all network nodes acting as share hosts and set permissions appropriately locally and let Windows Pass Through Authentication handle the rest (you don't have to log on as those users they just need to be there for permissions sake).
And it's not only Comodo or Zone Alarm that can cause network issues when it comes to sharing. I've done this stuff for nearly 20 years and just recently had my butt handed to me by AVG 2013. Took me close to an hour of trying everything I could think of until I finally removed AVG and like magic everything just worked again like it is suppose to. So if you are using any type of third party security suite consider removing it. At least until you have your networking issues resolved and then put it back and see what happens. Very often that's all it takes, uninstall, setup your network and make sure everything is working properly and then re-install. Some can take some more sophisticated tweaking to prevent it from interfering with Windows networking.