I have worked on a friends XPS gen 6, which is basically the same as the gen 5, and the massive green clad around the heatsink would not look very nice, and the EMI sheilding all over it would screw it up, becuase you would have to cut through that. The internals of the dells arent very nice, so I would just save the time and money to get your next system, or some way of better cooling for the thing, as those XPSses get TOASTY!
Ruan
Ruan