Done that before.I need to open a hex file in VB6 then
1.detect start of line (:)

2.Store next two hex digits ,which are length of data bytes into
a variable LENGTH

3.Store the next 4 hex digits in a variable ADDRESS

4.Next two digits are mostly zero for 8-bit mcu except EOF.So
check this byte for end of file. variable STATUS

5.This will be a loop in which store the address and data in a
array [address][data].Number of loops that it executes is
known by LENGTH variable.

6.After that just for check one can do checksum.this may be
optional

7.At the end of the whole processs one gets two dimensional array
having respective [address][data/opcode]

8.This will be than stored in excel file using VB.

9. Open that excel file and than sort the address column in ascending oder to get exact address and code.

10.If one wants then he can send address and respective data to
mcu using serial port and than program it.

This whole procedure can be done to any mcu (8-bit) and can be programmed in similar way.This can be further enhanced into a window based disassembler.