first off, its not recommended to power the xbox without the dvd drive connected. you should have the proper equipment. it is possible to use the xbox as power while flashing but it will flag your console and could lead to a ban (should you ever decide to go on live). if its a a hitachi or benq then its reletavely straight forward as long as your computer has a compatible sata. if not then a VIA6421 PCI-SATA card will be needed which can be picked up cheaply. if you arent going to power the flash with the xbox then you will need a CK3 (any type will do) and a spare molex or external psu and this will help with the power cycling.
assuming you havent updated to the latest dash then you can rgh your xbox to play backups straight from hdd and run unsigned code but this requires more equipment and some soldering ability... here is a guide
Reset Glitch Hack Guide using TX Coolrunner
flashing is much more simple and here is the tutorial
find out which drive you have and have a read of the jf tut folling the links specific to you