Help, with Text Field Acceptance,

hi,
i have a table in which i have many text boxes, they are named as a1,a2,a3,a4 to a16 the next row is b1,b2,b3 to b16 and so on up to G1,G2 etc, where the user enters his data, what i want to do is only allow the user to enter numbers, which can have decimals if required, how can this be done,
also i have another set of textboxes through which i want to loop and prevent user the user from entering the same data in more then one box how can this be done any help will be appreciated thank you.these are the text boxes a1,b1,c1,d1,e1 etc which is actually the first column in the table.
i have created the following array:
letterArray[0] = 'A'
letterArray[1] = 'B'
letterArray[2] = 'C'
letterArray[3] = 'D'
letterArray[4] = 'E'
letterArray[5] = 'F'
letterArray[6] = 'G'
how can i loop through to achive the above,
plz help i really need it, if u can help but need more info let me know plz.Than you.