Required- compatible SATA controller. Via 6421 (and onboard via of similar vintage) and Nvidia nforce 3 and 4 are the usual ones (VIA do external cards should you so desire). If you do not know what you have CPUz will tell you
http://www.cpuid.com/softwares/cpu-z.html
Optional depending on the person you speak to- Drive powering device. It is sata but has a custom power cable instead, you can build one (pinout on
http://forums.xbox-scene.com/index.php?showtopic=668247 ) or buy one (several options ranging from handmade version of the link a second ago to commercial ones like the maximus Xtractor and xecuter CK3)
You can however use your 360 itself to power the drive, it makes some things a bit more tricky (powering and ejecting the drive) but still very possible. Do remember to electrically join (use a wire, some tin foil or something) the 360 metal case and your PC case though. Some have said it might at the very least help flag you for a ban (the 360 knows it was powered without a dvd drive) but no real evidence has been found this is the case.
Very optional- case opening kit. torx screwdrivers sure but the case opening tool is optional- I usually use a poker and have a scalpel to hand.
Not necessary for benq- a liteon 7 series probe, 8v/9 series dual probe/switch kit or pogo ma thoin probe.
Alternative- these days all in one/standalone flashing devices exist if you want. They cost a lot more than a £10 SATA card though.
For what it is worth Benq and samsung drives are probably the easiest of all the 360 drives to flash.