Not sure .. but if the question is about the font size of the worksheet
tabs, then think it's a windows setting ("Scrollbar" size)
Say, in Windows XP:
Right-click at any empty spot in desktop > Properties
In Display Properties dialog, choose Appearance tab
Click "Advanced" button
In the Advanced Appearance dialog
Click the "Item" droplist > choose 'Scrollbar"
Set size to say: 25 > OK > Apply
