First you need to detect which drive you have, go http://www.llamma.com/xbox360/Xbox_360_DVD..._Comparison.htm
and look at that, compare your drive trey to one of the ones in there. Also, not that BenQ and the new Liteon have the same trey (Liteon = New Drive) So you will need to then, remove your faceplate and look at the wire that is in a small hole below your 360 dvd drive. Yellow = Liteon, Grey/White = BenQ. http://img.photobucket.com/albums/v251/the...nQorLite-on.jpg
Check that to get an idea of where the cable is.
Then, you need to discover what your chipset is (Device Manager -> IDE/Atapi Controllers), looking for something like Intel ICH*, or Nforce* and such. Depending on that, will depend on wether or not you need to buy a Via VT6421 card (about £10 on ebay), which you will then need to mount in your PC's PCI Port.
When you have all that, you need to think about the way you want to flash it, Dos Or Windows, if your on a 64bit windows OS your buggered for using windows. But if you can use Windows I would recommend using JungleFlasher.
When you get that far, let me know and I'll add more