After about 3 days of trying things and looking for an answer on the web, I finally found the solution. There is a tutorial here:
http://www.sevenforums.com/tutorials...ns.html?filter[2]=Networking%20Internet
The problem was that I had to go to "securities" first to change the security setting to "everyone." After that, I could share the folders, using the "share" option.
If anyone else has this problem, the above link should explain it well.