posts can only be seen by certin user groups or user id?
 

any way to do this?

you can modify Templates " postbit " ,

add $post[userid] , so you can see userid in post :p

i mean a special forum where users can post, but only i can see their posts, and they can only see theirs

This can be done in Admin CP/Forums&Moderators/Permissions.

For that specific forum, Choose "Use custom settings" and assign your user groups:
can view forum"-YES
Can view others' threads"-NO
Can reply to other's threads- NO
Can reply to own threads YES
Can edit own posts YES

Dont forget to enable access masks inside vbulletin options..

Enjoy..