Excel 2000 (or upgrade?)

Is there any way to get Excel to sort numbers (accounting categories)
as text, i.e., the sorted output would look like:

5
50
501
5011
5012
5013
51
511
5111
5112
5113
6

I get the correct sorting action if I replace the numbers with, e.g.,
letters A through J.

I don't want to fill in the right-hand digits with zeros, because that
would break something.

Simply formatting the cells as text doesn't work.

I'm using the account numbers, via cell range reference, in a SUMIF
formula's critera, that isn't hard coded, but gets the accounting
category to subtotal from the data in the cells to be sorted.

=FIXED(SUMIF(R4C8:R500C8,RC8&"*",R4C10:R500C10),2)

I don't want to break the above formula, where RC8 is the cell that
contains the account number. C8 contains the accounting category for
the individual transaction being posted, which account number is four
digits. If the account number has less than four digits, the value is
a sum of all transactions that have those first digits in their
account number.

TIA

Fred Holmes