Dosihris, The buttons are are disabled because you are not allowed to rearrange the columns of an already existing table. If you want to put the column in the 'middle' of existing columns you will have to drop and recreate the table (along with exporting / loading any data, recreating indexes, primary and foreign keys, etc.).
The Up and Down arrows are enabled when you are creating a new table. Since the physical object doesn't exist yet, you can rearrange columns however you want.