If you're used to flashing...
Very simple, use cracked phoenix (no pop up will show once you hit refurbish)
Please report if you were successfull or if you having any trouble.
Download and install Phoenix 2010.8http://www.megaupload.com/?d=HF2NA53Z2)
Download This hacked firmware (Split in 3 Sorry for that)
Part 1: http://www.megaupload.com/?d=528ED8YQ
Part 2: http://www.megaupload.com/?d=576G49D4
Part 3: http://www.megaupload.com/?d=V9DJDHX53)
Extract the folder in: “C:/Program Files(x86)/Nokia/Phoenix/Products/RM-596″4)
Connect N8, close ovi, run Phoenix5)
In Phoenix select "file" then "manage connections", use the arrows to put USB on top of priority list and hit "apply" then close6)
In Phoenix select "file" then "scan product", (Phoenix should at that point have found your n8), then hit "Flashing" then "Firmware Update"7)
In the firmware update screen, you’ll see that Phoenix has found the firmware files you installed in the folder in products (if it doesn’t find any firmware, add the directory C:/Program Files(x86)/Nokia/Phoenix in all the three boxes in Tools–>Options–>Product Location
now hit REFURBISH
Done Now you can install unsigned apps