How to use EXECUTE interrupt?

Hi,
This is the interrupt I want to use.
But I don't know what DS: DX should point to.

What's "DS: DX = pointer to an ASCIIZ filename" ?
Is there anybody who can explain and let me know what ASCIIZ filename is?

*************************************
INT 21,4B - EXEC/Load and Execute Program

AH = 4B
AL = 00 to load and execute program
= 01 (Undocumented) create program segment prefix and load
program, but don't execute. The CS:IP and SS:SP of the
program is placed in parameter block. Used by debuggers
= 03 load program only
= 04 called by MSC spawn() when P_NOWAIT is specified
DS: DX = pointer to an ASCIIZ filename
ES:BX = pointer to a parameter block

*************************************

Also here is another code.

pushad
mov     eax, cr0
push    eax
and     eax, 0FFFEFFFFh
mov     cr0, eax

;/////PUT PATCH CODE HERE/////

pop     eax
mov     cr0, eax
popad

Usng this code cause an exception in the program.
How can I apply this code withput getting any exception?
Also does changing the behaviour of CR0 register cause any problem for other programs or not?
I mean is this register global for all processes or is it just for the process that I'm running and changing CR0 in it?


Thanks in advance.
Regards,
Zest.