I use the CK3 Pro Connectivity kit from Team Xecuter and a SATA 6421 card to do my flashing. The only problem with using the 360 to power the drive is that M$ "can" flag it for being out of the console. Opinions differ on this. If you're not worried about being banned from XBL, then you have nothing to worry about.

Flashing with JungleFlasher is easy as pie, as long as you're not trying to read and flash certain Liteon drives.

Here's what the Team- X tutorial says about being flagged:

3. To program your DVD drive you need to take it out of the Xbox 360 case and then connect it to your PC. If you try to power your 360 DVD using your console it will get flagged as unconnected from the motherboard (center green light flashing on the ROL panel - this is a documented possible ban flag so be aware)

HERE IS THE TUTORIAL....Loads of information.