ya that adapter for the USB is all over the place, its like $25.00, it allows you to plug both sata, IDE 2.5 and IDE 3.5 into your USB and comes with the large power block.
the grey thing is the adapter (instead of using the connectivity kit) this is a different connector that will allow you to plug in power and SATA cable into the xbox360 drive.
I have been using and selling to PC repair people that USB adapter for a long time. it works great.
the USB version is not complicated. (been using that item for over 6 months).
take xbox360 HDD off unit.
plug the grey item into the xbox360 HDD connector
on the end of the grey item will be a power connector and a sata port.
plug the power connector into (and into the larger black item (12v+5v+GND power)
then plug the sata cable to the end of the grey item and then to the smaller black item (SATA, IDE 2.5 and IDE 3.5 connector).
then plug the large black item (into the wall for power)
then plug the silver USB Cable connected to that smaller black item into your USB port.
and you will then have access to that XBOX360 HDD via windows XP using xplorer360.
works great.