correct the expression of the textbox field

hi... to all..

i've written the code in expression field...

=format(sum(fields!salary.value),"##\,##\,##\,##\,##\,##\,##0.00")

the code is for printing the number in this format(12,23,23,34,123.00)

now i got an problem i.e if i give 5 digit the it will print ,,,,,12,123.00 the remaining commas 

are printed.. i dont want to print the extra commas.. how the word length is there that much it 

should take..i.e( for 5 digit 12,123.00 and for 9 digit 12,23,23,123.00)...

i've tried by removing some of the #'s but it is for fixed number.. 

please help me...