I had the same problem you did moonseak, and this is how I did it
since the xbox turns on the same time as my PC, I turn on the PC, and go into the BIOS
once in BIOS, I switch on the 360, put the enable0800 disc in, and let it run for 10-20 seconds
then I take it out, exit BIOS, and let windows load normally
so my BIOS is the PAUSE I'm able to do right before system startup, which allows me to run the enable0800 disc
hope I helped
You can also use the PAUSE/BREAK key to halt the system at post or any time, then hit the enter key when you are ready to continue.
This will save alot of time and trouble. You won't have to enter the bios and not every system has the boot menu option, but all have the Pause/Break key. Just a suggestion.