[NASM] Two files

[fka]

Hello. Everything I have to do is just changing some specific text from first file to another text. I have a clue - read first file character by character to array while character != space. After that compare array with my replacement text and decide what action will be performed. That's my whole idea. I wrote some code:

org 100h

start:
    mov     ax, 3D02h
    mov     dx, nameR
    int     21h

    mov     [readF], ax

    mov     ax, 3C02h
    mov     dx, nameS
    int     21h

    mov     [saveF], ax

read:
    mov     bx, readF
    mov     bp, 10h

    mov     ah, 3Fh
    mov     dx, buffer
    mov     cx, bp
    int     21h

    mov     ah, 2Eh
    int     21h

save:
    mov     bx, saveF
    mov     dx, buffer
    mov     ah, 40h
    mov     cx, bp
    int     21h

    mov     ah, 3Eh
    int     21h

theend:
    mov     ax, 4C00h
    int     21h 

nameS   db "new.txt", 0
nameR   db "s.txt", 0
readF   dd 0
saveF   dd 0
buffer: times 10h db 0

This code doesn't work :/ Compilation process is fine but program is not working. What's wrong with code above and is my idea correct?
I'm working on WinXP - 32b - NASM - x86.