How can i use imce to create a foler for a node to store files belong to that node??

This not possible with IMCE.

ufku is correct. That I know of the only placeholder available in IMCE is %uid

"Use %uid as a placeholder for user ID. Ex: users/user%uid creates directories such as users/user1, users/user42, etc."

You can do that with PHP though "If you want more flexibility in directory paths you can execute php to return a directory path.
For php execution your directory path must start with php: and the rest must be a valid php code that is expected to return the actual directory path.
Ex: php: return 'users/'.$user->name; defines users/USER-NAME as the directory path.
A multi-level directory example php: return date('Y', $user->created).'/'.date('m', $user->created).'/'.$user->uid; defines MEMBERSHIP-YEAR/MONTH/USER-ID as the directory path, resulting in self-categorized user directories based on membership date.
Note that you should use the $user variable instead of $GLOBALS['user'] since they are not always the same object." source: the description text at admin/settings/imce/profile

Another option is the module http://drupal.org/project/filenode

Closing 6.x-1.x issues as this branch is no more supported.