I really suggest reading JaredC01's thread
hereIt's worth reading through all 20 pages of it... everything that's been done is documented somewhere in there.
My diagram has 11-12 connected instead of 9-10 in order to get access to the higher HDTV modes on my monitor (720p and 1080i). Generally, if your monitor was made fairly recently it' should be able to display in those modes.
Enabling 480p will not keep your xbox from working on your tv.
It is possible to blindly turn on 480p (and you need to if you don't have an hdtv to hook up to do it). Instructions on this are in JaredC01's thread, roughly page 3 or 4 if my memory serves me.
In order to enable any of the hdtv modes (480p, 720p, and 1080i), you have to hook up an hdtv pack (or equivalently, connect pins 11-12 and 13-14). So if I were doing it again, I'd just make a VGA cable with pins 11-12 and 13-14 connected, follow the instructions in JaredC01's guide.
Just found it... page 7 (I was a little off)
QUOTE
You have to ground pins 11 - 12, and 13 - 14. That will give you the high def mode in the XBox dashboard.
To set 480p blindly in the XBox Dash:
Down
Down
A
Pause 1 Second
Down
Down
Down
A
Pause 1 Second
Down
A
Pause 1 Second
Left
A
Restart your XBox, and you should be in 480p.