I'd be careful about replacing the main fan with a low CFM 60mm one. The Xbox fan is a custom 70mm model that pushes around 30CFM (mine is anyway, it's an NMB fan Model number: 2810KL-04W-B50. 33.5dB 3800rpm 52.8m3/hr).
If you're in a warmer climate (like I am being in Australia) then you'll need to take care that you don't reduce the effectiveness of your cooling too much.
I'm looking at putting an 80mm fan in that does around 25cfm at 19dB but it will take a bit of case modding to do it and I wonder if it's worth it for a few dB.
Oh yeah, to remove it, you take out the hard disk and dvdrom trays, then using a small flat head screwdriver, lever out the black plastic clips and pull up. It pops out easily and doesn't use screws to be held in