This is something very interesting I found on the net, written by Premal (plmehta@vsnl.com)


An MS Excel Add-in to convert amount available in figures to words.
Installation
        Copy the attached file to the folder where excel stores the add-ins. (To know where excel stores the add-ins, open any workbook, click on Tools - Add-ins - Browse) 
        Then open an excel workbook. Click on Tools - Add-ins - Browse - Give the path to this Addin - Ok
Usage
You can use the functions AmtInWords and AmtInWordsUS in any worksheet. The syntax is:
=AmtInWords(decimal number/cell reference, [currency code/cell ref], [no. of decimals])
=AmtInWordsUS(decimal number/cell reference, [currency code/cell ref], [no. of decimals])
 
Explanation
The function AmtInWords gives the output in lakhs/crores
The function AmtInWordsUS gives the output in million/billion
The first parameter for these functions is compulsory  you can give a number or the reference of a cell containing a number (absolute or calculated)
The second parameter is the currency code. This is optional (the default is INR) and is to be given if you use a different currency than INR
The third parameter is the number of decimals in the fraction part. This is optional (the default is 2) and is to be given if it is different. At present, the accepted values are 0, 2 and 3
Examples
=AmtInWords(10000000)
=AmtInWords(123456.77)
=AmtInWords(123456.747, "OMR",3)
=AmtInWords(C4)
=AmtInWords(C4,A3) ' Where C4 contains a number and A3 a currency code
=AmtInWordsUS(B3) ' Shall give the amount in millions (US format)
=AmtInWordsUS(B3,"USD") ' Shall give the amount in millions (US format) and in US currency (Dollars)
=AmtInWords(C4,"GBP") ' Shall give the amount in lakhs and in UK currency (Pounds)
=AmtInWordsUS(B3,"OMR",3) ' Shall give the amount in millions and in Oman currency (Omani Rial) which has upto 3 decimals in the fraction part
Notes
The system shall NOT give you any warning/error if you use:
=AmtInWords(C4,"USD") ' Amount in lakhs and in US currency (Dollars)
OR
=AmtInWordsUS(C4,"GBP") ' Amount in millions and in UK currency (Pounds)
At present 6 currency codes are supported:
INR (the default ... not required to be given separately) 
USD (dollars) 
GBP (pounds)
EUR (euros)
OMR (Omani rials)
BDT (Bangladesh Taka)