I installed an 80 Gig Western Digital HDD in the Xbox and it worked fine, but then I saw a HDD that was cheaper though and I got it. It was a Maxtor HDD. I installed it in the Xbox and it didn't work. It wouldn't even let me boot original games. I've tried two other HDDs since then and none of the HDDs let me boot original games, EvoX on CDRW, or anything. The only HDD that lets me do stuff is the original Xbox HDD. I've tried every single jumper setting and I've even tried using different ribbon cables and have had no luck. I've also tried different Bios's.
BASICALLY: The Xbox won't work if a new HDD is installed but it will work if the old HDD is installed. Anything other than the new HDD won't even let me boot from the DVD-Rom.