Sort Unique, Then Copy From Original List

I have a CSV spreadsheet full of data: many rows and many columns. I want to sort based on values in some column. Then, I want to divide my large worksheet into smaller worksheets based on these sorted column values. For instance, if column 4 was 20,000 items long and contained 6 unique values I would want to create 6 smaller spreadsheets. Each spreadsheet would still have a column 4. Now, however, all the column 4 values would be the same for a particular spreadsheet. It would be nice to have a pop-up window query me for which column to use to divide the data with, instead of hardcoding a value in (like 4).

I am trying to crank this CSV file through MATLAB and it is just too big. My PC has 1GB memory and it still craps out. I am guessing that a dozen or so smaller files will be easier for MATLAB to digest. Any help is appreciated!

For the record, I am doing the following to sort a column, then copy it to a scratch worksheet and then determine all the unique values. I have hardcoded in column lengths and would really like to know how to make these variable expressions:

Sub divide_and_conquer()

Dim lngSheet As Long
Dim strName As String

Range("A1:HR778").Sort Key1:=Range("D2"), Order1:=xlAscending, Key2:= _
Range("B2"), Order2:=xlAscending, Key3:=Range("E2"), Order3:=xlAscending _
, Header:=xlGuess, OrderCustom:=1, MatchCase:=False, Orientation:= _
xlTopToBottom, DataOption1:=xlSortNormal, DataOption2:=xlSortNormal, _.............