Nam,
Has your worksheet been protected? This could be one reason that the merge
and centre option appears grayed out. Left click on Tools at the top of the
screen, roll over the Protection option to bring up the sub menu and if one
of the options says 'Unprotect Worksheet' then that is the problem. Left
click to unpretect the sheet and you will be able to merge and center. If
this is the problem dont forget to protect the sheet after you're done to
protect those formulas and layout.
Hope that helps.
