It's a pretty easy job (1/2 -1 hour) but there are a couple of things to watch out for. You can get a parts diagram at Xerox's website to follow along with the description, but hopefully it won't be strictly necessary. I've done this for a Phaser 860 but it should be essentially the same with your machine.
-Power down and remove the A/C plug.
-Remove the side covers.
-Remove the drum maintenance tray.
-Remove the drum maintenance tray guides - one on each side mounted to the frame. A single screw holds each one. If the one on the right side does not come out, manually rotate the x-axis motor gear to move the printhead toward the center of its travel until it's clear of the guide. IMPORTANT: When reinstalling the guides, make sure the jaws are engaged in the slots in the rear of the frame by visually inspecting them. Otherwise the maintenance drawer can become jammed and it may necessitate breaking the locking mechanism to free it!
-Remove the bright shiny duplex guide plate in front (two screws).
-Remove the upper feed roller assembly. First remove the clutch and belt on the left side (1 retaining clip). Remove
a screw on the right frame and the bearing retainer clip on the inside of frame on the left side, unplug the sensor cable connector and pull the roller/sensor assembly out. IMPORTANT: The assembly comes apart into two halves. Be careful not to drop one half and damage the sensor flags. If you do, epoxying them back together works fine (been there!) Try not to lose the bearing on the right side which will slide off the shaft (same with the left one).
-You now have access to the drum heater containing the bulbs. Unplug the harness to it on the outside of the right side frame. Remove the two silvery screws in front (not the brass colored ones) to extract the heater assembly. IMPORTANT: If you take the heater assembly apart, which is unecessary to replace the bulbs, it can be devilishly hard to put it back together - you have to hold several things together, which don't seem to naturally want to stay together, while putting the screws back in.
Of course, don't touch the glass part of the replacement halogen bulbs with your bare fingers (or wipe them them clean if you accidently do).
When reassembling make sure the bearings for the upper feed roller assembly are fully seated into the holes in the frame. It's not difficult but it can take a little time to get both of them seated while holding the assembly together.
I hope this covers it all. Not to worry, I'm sure you'll figure out how to deal with anything I may have left out.
Jim