mov ebx, offset liczba

    mov al, [ebx]
    shl eax, 8

    mov al, [ebx+1]
    shl eax, 8

    mov al, [ebx+2]
    shl eax, 8

    mov al, [ebx+3]


-------------------------------


    mov edx, 12345678h

    xor eax, eax

    mov ecx, 0ff000000h
    and ecx, edx
    shr ecx, 24
    or eax, ecx

    mov ecx, 00ff0000h
    and ecx, edx
    shr ecx, 8
    or eax, ecx

    mov ecx, 0000ff00h
    and ecx, edx
    shl ecx, 8
    or eax, ecx

    mov ecx, 000000ffh
    and ecx, edx
    shl ecx, 24
    or eax, ecx