fakeipx.asm

code:
org 0x100
mov dx, msg
mov ah, 9
int 0x21

;get int2f dos  handler

mov ax, 0x352f
int 0x21
mov [old_addr_seg], es
mov [old_addr_off], bx

;set handler 2f
mov ax, 0x252f
mov dx, handler_dos
int 0x21

;set handler 7a
mov ax, 0x257a
mov dx, handler
int 0x21

;Terminate and stay resident
mov dx, (((end - code)+15)/16)+16
mov ax, 0x3100
int 0x21

handler:
sti
mov ax, 0
iret

handler_dos:
;override ipx test ax==0x7a00
pushf
cmp ax,0x7a00
je override

;call old interupt handler
popf
jmp far dword [cs:old_addr_off]

override:
mov ax, 0xff
sti
popf
iret

old_addr_off dw 0
dummy        dw 0
old_addr_seg dw 0
end:
msg db "FakeIPX Installed :) to uninstall, restart :(", 10, 13, '$'