1) not possible "out of the box" (there might be a MOD, check the MODs forum), it's all done via the permission system:
How to Create a Private Forum
2) what errors? You don't need a smilie pack to install new smilies.
Upload the smilie images to (e.g.) images/smilies/ (specified in Admin Panel --> General Admin --> Configuration) and go to the Admin Panel -> Smilies Admin. From there, click the Add a smiley button, select the filename from the list and add the smiley text and smiley code.
If you have downloaded a smiley packet that includes a pak-file, you can import the pak file (but you still have to upload the images.